Invertebrate Anatomy OnLine
Periplaneta americana ©
Copyright 2004 by
is an exercise from Invertebrate
Anatomy OnLine , an
Internet laboratory manual for courses in Invertebrate Zoology. Additional
exercises can be accessed by clicking on the links in the column to the left. A
glossary and chapters on supplies and laboratory techniques are also available. Terminology
and phylogeny used in these exercises correspond to usage in the Invertebrate
Zoology textbook by Ruppert, Fox, and Barnes (2004). Hyphenated
figure callouts refer to figures in the textbook. Callouts
that are not hyphenated refer to figures embedded in the exercise. The glossary
includes terms from this textbook as well as the laboratory exercises.
Mandibulata sP, Tracheata,
Hexapoda SC, Insecta C,
Dicondylia, Pterygota, Metapterygota, Neoptera, Blattaria O,
Blattoidea SF, Blattidae F,
Blattinae sF (Fig
16-15, 20-14, 20-15, 21-23)
by far the largest and most diverse animal taxon, includes chelicerates,
insects, myriapods, and crustaceans as well as many extinct taxa. The
body is segmented and primitively bears a pair of jointed appendages on each
epidermis secretes a complex cuticular exoskeleton which must be molted to
permit increase in size. Extant
arthropods exhibit regional specialization in the structure and function of
segments and appendages. The body is typically divided into a head and trunk, of
which the trunk is often itself divided into thorax and abdomen.
gut consists of foregut, midgut, and hindgut and extends the length of the body
from anterior mouth to posterior anus. Foregut
and hindgut are epidermal invaginations, being derived from the embryonic
stomodeum and proctodeum respectively, and are lined by cuticle, as are all
epidermal surfaces. The
midgut is endodermal and is responsible for most enzyme secretion, hydrolysis,
coelom is reduced to small spaces associated with the gonads and kidney. The
functional body cavity is a spacious hemocoel divided by a horizontal diaphragm
into a dorsal pericardial sinus and a much larger perivisceral sinus. Sometimes
there is a small ventral perineural sinus surrounding the ventral nerve cord.
hemal system includes a dorsal, contractile, tubular, ostiate heart that pumps
blood to and from the hemocoel. Excretory
organs vary with taxon and include Malpighian tubules, saccate nephridia, and
organs also vary with taxon and include many types of gills, book lungs, and
nervous system consists of a dorsal, anterior brain of two or three pairs of
ganglia, circumenteric connectives, and a paired ventral nerve cord with
segmental ganglia and segmental peripheral nerves. Various
degrees of condensation and cephalization are found in different taxa.
is derived with centrolecithal eggs and superficial cleavage. There
is frequently a larva although development is direct in many. Juveniles pass
through a series of instars separated by molts until reaching the adult size and
reproductive condition. At
this time molting and growth may cease or continue, depending on taxon.
includes arthropods in which the third head segment bears a pair of mandibles. As
currently conceived this taxon includes myriapods, hexapods, and crustaceans. Appendages
may be uni- or biramous and habitats include marine, freshwater, terrestrial,
and hexapods share tracheae and a single pair of antennae and are sister taxa in
which have gills and lack tracheae, are excluded and form the sister group.
body is divided into three tagmata; head, thorax, and abdomen. Appendages
are uniramous and a single pair of antennae is present. Three
pairs of legs and two pairs of wings are found on the thorax of most adults. Hexapod
legs are uniramous although there is increasing evidence that they evolved from
multiramous appendages of their ancestors. Gas
exchange is accomplished by trachea. Excretory
organs are Malpighian tubules and the end product of nitrogen metabolism is uric
is relatively little cephalization of the nervous system. Insects are gonochoric
with copulation and internal fertilization.
hexapods are insects. A
few hexapod taxa (orders) lack wings and have primitive mouthparts recessed into
the head and belong to Entognatha, the sister taxon of Insecta. Insects
have ectognath mouthparts and the adults (imagoes) of most taxa have wings.
are the winged insects. These insects are derived from a winged common ancestor. Adults
of most taxa have wings although they have been lost in some.
are fast running insects probably closely related to termites (Isoptera ). Some
primitive taxa have endosymbiotic gut zooflagellates similar to those of
termites. The tarsi are five-articulate. The oval body is dorsoventrally
depressed and most the head is hidden from dorsal view by the large pronotum. The
antennae are long and filamentous. Most taxa have wings, in at least one sex,
but they are not always functional. Eggs are enclosed in a proteinaceous ootheca
which may be gestated internally, brooded externally, or deposited without
further maternal attention. Most
cockroaches are tropical and several species are pests in or near buildings
especially in warm climates. It
is often found in homes and in my experience in the southeastern US, it is
common in zoology laboratories, especially in those in older buildings.
americana, the American cockroach, the largest widespread North American
cockroach, reaches 44 mm in length. It is dark reddish-brown with a pale
peripheral band around the pronotum. Adults
have large wings and can fly, although they do not often do so. Nymphs, of
course, are wingless. It is easily, albeit unintentionally and regretfully,
spread by human commerce and is worldwide in warm climates and, in heated
buildings, cosmopolitan. Periplaneta is
nocturnal, negatively phototactic, and prefers dark warm, moist habitats. It is
acutely sensitive to vibrations and is one of the world’s fastest running
insects, as you know if you have tried to stomp one in the kitchen late at
night. Periplaneta americana is
one of several cockroaches found near (peridomestic) or in (domiciliary) human
habitations. Such insects are referred to as synanthropic (= with man). Several
of the most common North American synanthropic species are discussed below. Any
of these species could be used for this exercise but other species of Periplaneta differ
the least from this account and for our purposes are interchangeable with P.
life cycle consists of egg, numerous nymphal instars (6-14), and the adult, or
imago. Blattarians are paurometabolous with nymphs closely resembling small
adults except for the absence of wings. Paurometabolous
insects have no pupa or metamorphosis. The eggs are laid in a tough, sclerotized
protein case, the ootheca, normally containing 16 eggs. Females average one
ootheca per month for most of the year but may exceed that average during
periods of peak reproductive activity. Nymphs lack functional wings, of course,
but wingpads appear in the 4 th instar
and gradually increase in size with each molt. The
life span is 2-3 years with only the last year being spent as an adult. Adults
live for about a year.
omnivorous, opportunistic, scavenging species feeds on almost anything organic,
plant or animal, but prefer starches and sugars. Adults and nymphs have similar
population density is controlled naturally by several species of parasitoid
wasps including Evania and Aprostocetus. Both
are egg parasitoids in which the female wasp oviposits in the roach ootheca
where the wasp larvae hatch and feed on roach eggs. Evania is
a distinctive, small, black wasp with a laterally flattened triangular abdomen
that waves flag-like (hence the common name “ensign" wasp) as the adult walks. Adult Evania are
about 1.5 cm in length. The
female, with great difficulty, inserts one egg in each ootheca. The
larva hatches and consumes all 16 roach eggs before achieving a length of 8 mm,
pupating, and emerging from the now empty ootheca. Adult Aprostocetus are
tiny, about 2 mm long. Both species are stingless and no threat to humans. Small
wasps, especially those waving a flag, seen in roach-infested areas should be
protected and encouraged, not killed. Attempts to control roach populations with
pesticide sprays can be counterproductive because they indiscriminately kill
parasitoids in addition to the roaches. Roach
pellets (“roach hotels”), which are selective, are more effective.
are not biological vectors for human disease although they can serve as
mechanical vectors simply by harboring infectious organisms such as Ascaris eggs,
bacteria, or protozoan cysts on their body surfaces. The American cockroach is
the host for the cystacanth stage of the rat intestinal acanthocephalan, Moniliformis
The Major Synanthropic
species of cockroaches enjoy close synanthropic associations with humans and
have been spread throughout the world by human migrations and commerce and are
now serious pests. All
these species are thought to have originated in Africa. Many other species are
loosely associated with humans and their activities.
American cockroach, Periplaneta
americana , despite its
specific and common names, is an exotic that was introduced to North America
from Africa in the early 17 th century. It
is the largest of the domiciliary species, reaching 44 mm in length. Both
sexes have fully functional wings but rarely fly. The
pronotum is bordered by a pale yellowish margin. It
is easily confused with P. bunnea.
The last article of the cercus of P.
americana is over twice as long
as wide (Fig 16) whereas that of P.
brunnea is less than twice as
long as wide (Fig 14). Periplaneta
americana is the second most
abundant cockroach pest in the United States.
fuliginosa (smoky brown
cockroach) is an introduced peridomestic species. It
is common in the southern United States mostly found out of doors or in crawl
spaces or unheated buildings such as outhouses or garages. It
also occurs in buildings in the south and can be found further north in heated
buildings. In some localities it may account for almost 80% of cockroaches
captured near homes. The color is uniformly dark brownish black and it lacks the
pale pronotal margin of other synanthropic Periplaneta. Nor
does it have pale areas on the forewings that distinguish P.
australasiae. It reaches 35 mm in length, not quite as large as P.
cockroach) is an African native spread by human travel and commerce. It
is common in the southeastern United States, sometimes moreso than P.
americana, but it is usually
found outside. This species has a pale border around the pronotum as do most Periplaneta but
it lacks the pale areas on the forewings characteristic of P.
australasiae. It reaches 37 mm in length. Both sexes are winged and can
cockroach) is almost as serious a domestic pest as is P.
americana. It probably arose in Africa and spread throughout the tropics
and subtropics and is now circumtropical. It
is the most common domiciliary cockroach in Florida and although it occurs
farther north it is intolerant of the cooler temperatures tolerated by P.
Americana. It is similar to P.
americana but slightly smaller,
reaching 35 mm in length. It
is reddish brown, like P.
our other Periplaneta species,
its forewings have a pale yellowish band on the proximal anterior edge. Both
sexes have wings and fly. The specific epithet “australasiae” means
“south Asia”, not Australia.
cockroach, black beetle, water bug) probably originated in North Africa and has
become a common pest in the southern, midwestern, and northwestern United States
but is known as far north as southern Canada, the Netherlands, and Britain. It
prefers cool, moist habitats. Males
are winged, females have tiny vestigial wings, and neither is capable of flight.
Individuals reach 27 mm in length. Its
color is dark, almost black, and it prefers moist habitats. Blatta lacks
an arolium on its tarsi and cannot climb smooth surfaces. The
common name “water bug” derives from its preference for wet areas.
German cockroach, Blatella
germanica , originated
in Africa and traveled first to Europe and from there to North America. It is
the most abundant domiciliary cockroach in the United States and is an important
15 mm, it is much smaller than the Periplaneta species. It
is pale brown with two dark longitudinal bands bordering the pronotum.
banded cockroach) is assumed to have originated in Africa. It
is always found in buildings (except in Africa). It
was originally introduced into the Florida and spread north hitchhiking on fruit
shipments and in the luggage and automobiles of tourists returning north after a
is now found throughout the contiguous United States. This is a small roach,
reaching only 14 mm, and similar in size and general appearance to Blatella
germanica. The forewings cover the abdomen of the male but those of females
are shorter and the posterior abdomen is left uncovered. Two pale bands extend
transversely across the dark abdomen but these may be difficult to see with the
wings folded at rest. They
are obvious in the wingless nymphs. Supella lacks
the longitudinal stripes on the pronotum characteristic of Blatella.
The lateral margins of the pronotum of Supella are
available at modest cost, alive or preserved, from biological supply companies. It
can also be captured locally in homes or university buildings. Look
for it in warm, moist, dark places such as basements, drawers, wood piles,
sewers, sunken water meter enclosures, and compost piles. In
the home it can be found wherever there is food, including the usual debris on
the kitchen floor and under the refrigerator, on unwashed dishes left overnight
in the sink, and even in your library where it eats the bindings of your
favorite books. Female Periplaneta are
distinguished from other genera by having a divided 7 th sternite.
may be dissected alive and anesthetized, recently sacrificed and unpreserved, or
sacrificed is preferable unless you anticipate making physiological
observations, in which case the specimens should be alive and anesthetized.
Living specimens may be sacrificed in a covered dish with a cotton ball dampened
with ethyl acetate. Living
specimens should be anesthetized using chloroform, ether, or carbon dioxide. Sacrificed
specimens should be immersed in water or 80% ethanol (or 40% isopropanol) in a
small dissecting pan.
both external and internal anatomy are to be studied it is advantageous to have
separate specimens for these two undertakings. The
study of external anatomy is likely to damage the specimen to such an extent
that it will not be useful for studying internal anatomy. Students
should have access to both sexes, either their own specimens or by sharing with
a lab partner.
of Periplaneta are
elongate, oval in outline and strongly dorso-ventrally depressed, or flattened.
The body is divided into the three tagmata characteristic of insects, i.e. head,
thorax, and abdomen (Fig 21-1C). The
head is inconspicuous in dorsal view but the pronotum of the thorax is very
remainder of the thorax and abdomen are hidden by the two pairs of wings. Six
pairs of similar, strong, spiny legs are present.
a recently sacrificed or preserved cockroach with the dissecting microscope. The
specimen may be dry or submersed in liquid.
Figure 1. Dorsal view of a female smoky brown
cockroach, Periplaneta fuliginosa,
from Greenwood, South Carolina. Blatt37L.gif
Little of the head can be
seen in dorsal view (Fig 1). Position the specimen with the ventral surface up
and examine the head with the dissecting microscope. The head is
flattened dorsoventrally and is more or less pear-shaped in outline with the
mouthparts extending posteriorly from the narrow end of the pear. The head is
normally carried with its flat front surface, the face, held horizontally facing
the substratum (Fig 2). In
this position the mouth opens posteriorly, the mandibles project posteriorly,
and the palps touch the coxae of the forelegs. When
feeding, the flattened face is
held vertically with the mouthparts located ventrally, toward the substratum. The
flattened face is the anterior aspect of the head even though it is oriented
the thin edge of the broad end of the pear is dorsal, even though it is normally
held in an anterior position. When
in the feeding position the face is held anteriorly and the thin edge is dorsal.
Cockroaches have typical
unspecialized mouthparts and provide a good example of the primitive insect
mouthparts adapted for biting and chewing (Fig 21-1A,B). The
head can be retracted beneath the prothorax.
Figure 2. Anterior view of the
head of Periplaneta fuliginosa.
head consists of a complex of fused sclerites, which constitute the epicranium,
or head capsule, associated
with unfused sclerites and appendages. This hard sclerotized capsule encloses
the mouthpart muscles, brain, and anteriormost region of the gut and provides
sites of attachment for the mouthparts and antennae.
The head capsule is divided into several regions. Locate
the large compound eyes on
the dorsal edge of the head (Fig 1, 2). The antennae arise
on the face immediately ventral to the eyes. These
are useful as convenient, easily recognized landmarks.
suture marks the junction of
three fused sclerites that form the face. In Periplaneta this
suture is usually visible as a faint, yellow, Y-shaped line on the face (Fig 2)
but sometimes it cannot be found. The two arms of the "Y" begin at the antennal
sockets and converge between the two eyes. From
the convergence the single stem of the "Y" extends dorsally between the eyes
over the top of the head. It
divides the top of the head into a pair of sclerites, the epicranial
plates (Fig 2). The part of
the capsule between the two arms of the “Y” is thefrons, or
front, of the capsule (Fig 2). The frons is an unpaired sclerite.
Two white circular areas between the antennae and compound
eyes, at the ends of the arms of the epicranial suture, are the fenestrae and
are the vestiges of the ocelli of other insects (Fig 21-1A). Two
additional pale circles on the frons, ventral and a little medial to the
fenestrae, mark the sites of muscle insertions inside the capsule.
which is a region, not a sclerite, occupies the dorsum of the capsule between
the two eyes. It is divided in two by the stem of the epicranial suture (Fig 2)
and includes the two epicranial plates. In
some insects the posteriormost region of the vertex may be a distinct sclerite
referred to as the occiput.
The clypeus (KLIP
ee us) is an unpaired sclerite on the face (Fig 2, 21-1A). It
lies ventral to the frons and the two are joined along a transverse,
indistinguishable suture. The
clypeus is not movable.
third unpaired sclerite, the labrum,
is attached along a transverse, movable articulation with the ventral edge of
the clypeus (Fig 2). The
labrum is equipped with muscles and is movable. It
forms the anterior wall of the preoral cavity into which the mouth opens. The
labrum is usually considered to be derived from a sclerite of one of the head
segments but some entomologists believe it to be homologous to a pair of fused
appendages, similar to the labium in this regard.
sides, or cheeks, of the epicranium are formed by the paired genae.
In the cockroach these form the thin lateral edges of the head ventral and
posterior to the eyes. The
genae are formed of several indistinguishably fused sclerites.
the head capsule is penetrated by a large circular opening, the foramen
magnum through which pass
the gut, salivary ducts, and nerve cord. The foramen is bordered by the vertex
dorsally and the genae laterally. The
soft, cervix, or
neck, extends posteriorly from the foramen. Because
of the attachment of soft tissue of the cervix to the head capsule, the foramen
is not visible externally. Ventrally
slender, transverse cervical
sclerites are embedded in
the otherwise soft integument of the cervix.
anteriormost head appendages are the two antennae. These arise from a socket ventral
to the compound eyes. The
first article of the antenna is the scape and
the second is thepedicel (Fig
the pedicel arises a long, whiplike, sensory flagellum of
75-90 articles. The
antennae are equipped with mechanoreceptors but apparently not with
Ventrally the mouthparts surround and enclose a chamber, the preoral
cavity, from which the mouth opens (Fig 21-7). As
its name suggests, the preoral cavity precedes the mouth and is not considered
to be part of the gut, although both mechanical and chemical digestion begin
With the specimen positioned with its ventral side up, grasp
the labrum and mandibles with a pair of fine forceps and pull the head into the
feeding position (i.e. with the anterior face anterior, and the mouthparts
the labrum and look beneath it using a second pair of forceps or a fine needle
to move structures aside as needed.
The labrum, which you are currently holding aside, is the
anterior wall of the cavity. The
heavy, toothed mandibles and softer maxillae are its side walls and the labium
is its posterior wall. A
soft, tonguelike, mostly unsclerotized outgrowth of the ventral body wall, the
hypopharynx, extends into the preoral cavity immediately posterior to the mouth. Move
the mandibles and maxillae aside and find the mouth opening
dorsally from the preoral cavity immediately anterior to the hypopharynx.
The two mandibles lie
beside the mouth and form the lateral walls of the preoral cavity (Fig 2, 21-1A,
B). They are derived from a pair of segmental appendages. Each mandible consists
of a single article bearing a sclerotized, distal, cutting surface. The cutting
edge of the mandible consists of a lateral shearing incisor with
three or four sharp denticles and
a more medial grinding molar (Fig
The mandible is largely hidden from view but can be glimpsed
on the side of the head ventral to the gena and lateral to the clypeus (Fig 2,
forceps carefully lift the labrum and peer beneath it to get a better view of
the mandible. Its
dark, heavily sclerotized denticles are visible in this view.
The mandible articulates with the head capsule by two ball
and socket-like condyles, one anterior and one posterior (Fig 3, 4). The anterior
condyle can be seen at the
dorsolateral corner of the clypeus, on the face. The posterior
condyle articulates with the
ventral corner of the gena and can be seen on the side of the head capsule. Its
plane of motion is transverse, perpendicular to the long axis of the body. Movement
in this plane brings the two mandibles together on the midline. In contrast,
vertebrate mandibles oppose each other by moving in the vertical plane. Observe
the mandible with the labrum moved aside and imagine the motion of the two
mandibles with respect to each other. Grasp the mandibles with forceps and move
them in their preferred plane of motion. If desired, one of the mandibles can be
removed for closer examination.
Figure 3. The left mandible. A. Anterior view. B.
Posterior view. Blatt39L.gif
Look at the head from the side and find the maxilla (Fig
2, 21-1A,B). Like
the mandibles, the two maxillae are paired appendages lying beside the preoral
maxilla can be recognized by its large 5-articulate palp (the labium also has a
palp but it is much smaller and has three articles). Each
maxilla consists of a proximal cardo that articulate with the head capsule and a
distal stipes from which arise several processes.
Figure 4. Oblique
view of the head from the left showing the articulation of the mandible with the
head capsule of P. fuliginosa. The
labrum has been drawn as if transparent to reveal the left mandible beneath it. The
right mandible has been omitted for clarity. Blatt40L.gif
The cardo in
a short transverse partly sclerotized article extending laterally from the head
capsule (Fig 5). It
is inconspicuous because it is hidden by the larger stipes. The stipes is
easily seen when looking at the head from the side. It
is elongate and articulates with the cardo proximally, beside the ventral edge
of the eye. Distally
three processes arise from the stipes.
Most obvious of these processes is the maxillary
palp consisting of five
palp is sensory with chemo- and mechanorecepotors used to evaluate the
suitability of potential food. From
the distal end of the stipes arise a lightly sclerotized, lateral galea and
median, sclerotized, bladelike lacinia, which
bears denticles distally. The
lacinia assists the mandible in cutting food into smaller particles. The lacinia
is completely hidden by the soft bulbous galea. The galea acts as a sheath to
cover the lacinia and because of it, the lacinia is not visible until the galea
is moved aside. You may remove one of the maxilla for closer study if desired.
insect labium, also known as the second maxilla, is formed by the fusion of the
posteriormost pair of head appendages. The labium is the posterior wall of the
preoral cavity. It is best viewed by lifting the head to reveal its posterior
surface. The labium consists
of a large, platelike, proximal submentum (Fig
6, 21-1A,B). Articulated
with it is the similarly platelike, but smaller, mentum. Submentum
and mentum are the fused regions of the ancestral appendages. Arising
from the distal edge of the mentum is a pair of prementa,
the homologs of the original two appendages. Each
prementum bears a distal median glossa with
a lateral paraglossa beside
glossae and paraglossae are together known as the ligula and
function in the manipulation of food. A
3-articulate labial palp arises
laterally from the side of each prementum. The
palp is chemo- and mechanosensory. You
may remove the labium and examine it with higher magnification if you wish.
Figure 5. Posterior view of the left maxilla of P.
fuliginosa with the galea moved
slightly to reveal the lacinia. Blatt41L.gif
or tongue, is a long, process protruding from the ventral wall of the head into
the preoral cavity (Fig 7, 21-7). It is not a segmental appendage being instead
a fold of the body wall. It can be seen by looking into the preoral cavity,
either ventrally by spreading the mouthparts aside, or posteriorly by lifting
(or removing) the labium. The
hypopharynx divides the preoral cavity into an anterior cibarium and a posterior
thorax is the tagma specialized for locomotion and as such bears three pairs of
legs and, in adults, two pairs of wings and houses the muscles to operate them
(Fig 16-2). It is the middle tagma of the body and consists of the anterior
prothorax, middle mesothorax, and posterior metathorax, of which the prothorax is
by far the largest and the only one visible in dorsal view. In
ventral view the prothorax, mesothorax,
and metathorax are
all visible and easily recognized by virtue of the pair of walking
legs carried by each
Figure 6. Posterior view of the labium. Blatt42L.gif
Figure 7. Anterior view of the hypopharynx of P.
clypeus, labrum, left mandible, and labium have been removed for clarity.
large powerful legs are responsible for the cursorial competency for which
cockroaches are renown. Three pairs are present, of course, one on each thoracic
segment (Fig 8). The
three pairs are similar but increase in size from anterior to posterior. Each
consists of a large, flattened, proximal coxa,
a small trochanter,
a long femur, a tibia,
and a long tarsus (Fig
9, 21-1E). The
femur and tibia bear strong spines.
The tarsus is a series of 5-articulate tarsomeres. Tarsomeres
1-4 each bear a posterior
pad-like adhesive pulvillus. Tarsomere
5 ends with a pair of tarsal
claws beside a pad-like arolium. This
distal arrangement of claws and arolium is sometimes referred to as the
pretarsus. The arolium is an adaptation for clinging to smooth surfaces and
makes it possible for Periplaneta to
climb smooth walls.
Figure 8. Ventral view
of a female P. fuliginosa. The
distal articles of the legs have been removed for clarity. S = sternite, T =
When flexed, the femur fits neatly into a recess in the
surface of the coxa (Fig 8). The articulations between coxa and trochanter and
between femur and tibia are dicondylic joints which restrict movement to a
single plane (as, you may recall, does the dicondylic joint between the mandible
and head capsule). The coxa-body articulation is monocondlyic and permits
movement in a variety of planes as is the tibia-tarsus articulation. Dicondylic
joints are functionally similar to the hinge joints in your knee and elbow
whereas monocondylic joints function like ball and socket joints in your
shoulder and hip.
meso- and metathorax of adults of both sexes of Periplaneta each
bear a pair of large wings. The
anterior mesothoracic wings, or forewings (=
wing covers, often known as tegmina in orthopterans and blattarians), are
obvious in dorsal view whereas the equally large metathoracic wings (hindwings)
are almost entirely hidden by the forewings (Fig 10). The heavier,
parchment-like forewings protect the more delicate hindwings. The
hindwings are membranous and fold in pleats when at rest under the forewings.
The folded wings completely cover the dorsal surface except for the head and
Fig 9. Ventral view of the right midleg of P.
forceps and your fingers to extend the wings and examine their shape and
the way in which the hindwing folds when at rest.
nymphs, like immatures of other insects, lack wings, but like other pauro- and
hemimetabolous insects, develop wing
pads in older instars (Fig
11). The wing pads are transformed to functional wings by the last molt.
thorax consists of three segments but your view is obscured dorsally by the
wings and ventrally by the walking legs, especially their coxae. Each
segment has the expected complement of sclerites consisting of dorsal tergite
(or notum), lateral pleurites, and ventral sternites.
ventral surface of the thorax consists of large expanses of unsclerotized,
flexible, white exoskeleton in which are embedded myriad hard, golden brown,
the specimen on its back with a #1 stainless steel insect pin through the margin
of the pronotum. Move
the legs aside as needed to reveal the ventral surface of the thorax. The
proximal end of the coxa of each thoracic limb articulates with a complex of
sclerotized pleurites (Fig
12, 21-1D). On
the midline, between the right and left pleurites, lies a series of thoracic
sternites. Theprosternum is
a small, triangular, median, unpaired sclerite in the center of the prothorax,
between the clusters of prothoracic pleurites. The mesosternum is
more complicated than the prosternum and consists of several sclerites including
a large bilobed anterior plate followed by two slender posterior sclerites. The metasternum is
similar to the mesosternum except that the bilobed plate is completely divided
into a pair of plates.
Figure 10. Dorsal view of a female P.
fuliginosa with the wings
removed or extended to reveal the dorsal surface of the thorax and abdomen. The
abdomen has been stretched slightly to reveal tergites 8 and 9 which are
normally hidden under tergite 7. blatt46L.gif
thorax is equipped with two pairs of spiracles which open into the tracheal
respiratory system. The spiracles are
lateral and belong to the mesothorax and metathorax although they have migrated
anteriorly (Fig 12). Consequently,
the mesothoracic spiracle is
on the posterior prothorax and the metathoracic
spiracle is in the membrane
between the mesothorax and metathorax.
the dorsal thorax by moving the wings aside. The pronotum is
not obscured by wings and is always easily seen. It
forms a large shield behind the head and may be mistaken for the head by the
is heavily sclerotized and dark in color with a pale border. The mesonotum (Fig
10) is a transverse, lightly sclerotized plate covering the dorsal surface of
the mesothorax. The metanotum is
similar and covers the mesothorax.
The abdomen is
the largest of the three tagmata and contains most of the viscera. Its
segmentation is conspicuous both dorsally and ventrally once the wings have been
abdomen consists of 11 segments of which the 11 th is
reduced and fused with the 10 th so
that a maximum of ten segments are distinct and visible (Fig 21-1F). Further,
some of the segments, especially in females, are highly modified or in
unexpected locations and are not immediately visible and countable.
Figure 11. A late instar, 24 mm Periplaneta nymph.
first seven segments, known as the pregenital, or visceral, segments are
similar, unspecialized, visible and countable. Segments
9 in males and 8-9 in females are the genital segments and are modified for
reproductive functions. Segment
10 (and the vestigial 11) are postgenital and are also modified.
each segment is covered by a sclerotized tergite and,
similarly, is covered ventrally by a sclerotized sternite. Consecutive
sternites articulate with each other by unsclerotizedarticular membranes (Fig
tergites and sternites are connected by unsclerotized flexible pleura.
the dorsum of the abdomen and find the abdominal
tergites (Fig 10). Those
of segments 1-7 are similar in size and easily distinguished but tergite
8 is smaller and tergite
9smaller still. These
two tergites are usually telescoped under tergite 7 and may be difficult to see
until you lift tergite 7. Tergite
10 is a large posteriorly
bilobed plate overhanging the anus (Fig 10). Tergite
11 is fused with tergite 10. The bilobed posterior extension of tergite 10 is
sometimes referred to as the epiproct,
which is homologous to the tergite of segment 11 (Fig 10, 21-1F).
the ventral surface of the abdomen (Fig 12, H). Sternite
1 is a small sclerite lying
on the midline between the hindleg coxae. Sternites
2-6 are elongate, more or
less rectangular, sclerotized plates covering the ventral surface of the
7-9 of males resemble
sternites 2-6 but the posterior sternites of females are very different. In
females the posteriormost visible sternite is the large, highly modified sternite
7 (Fig 12, 13). Sternites
8, 9 are internalized under tergite 7 and cannot be seen without dissection.
Figure 12. Ventral view of a female P.
fuliginosa with the right legs
removed to reveal the ventral body surface and its sclerites. The
position of the abdominal spiracles under the overhang of the preceding sternite
is indicated. Blatt48L.gif
The anus is
on segment 11 and lies ventral to the epiproct (tergite 11). It is flanked by a
pair of triangular sclerites, the paraprocts (Fig
14, 21-11B, 21-12B,C) which are modifications of sternite 11. Sternite
10 is vestigial.
abdominal segments lack appendages but segment 10 bears a pair of large,
which are visible in both dorsal and ventral views (Fig 8, 13, 21-1F). Embryologically
the cerci arise as the appendages of the 11 segment but in adults are attached
to segment 10 since segment 11 has fused with segment 10. The cercus, although
segmented, does not contain intrinsic muscles. Extrinsic muscles, however,
extend from the cercus to the abdomen so it is capable of motion. Cerci
bear vibration-sensitive hair sensillae sensitive to air movements, including
sound, and perhaps to ground vibrations.
pairs of spiracles are present in the abdomen and are much smaller than the
thoracic spiracles. The abdominal spiracles are
located laterally on the anterior-dorsal corner of the pleura of the first eight
abdominal segments (Fig 12, 14, 21-1D,F). Lift
the free posterior edge of a sternite and look at the antero-lateral corner of
the following tergite to see the spiracle. It will be a small white oval. Abdominal
spiracle 1 is on the lateral
edge of tergite 1 rather than at the corner (Fig 12).
the dorsum of the posterior abdomen of a female. The
tergites of the genital
segments (abdominal segments
8, 9) are reduced and their tergites are largely hidden by the overhang of tergite
7 (Fig 10). Tergite
10 (fused with tergite 11)
is a large, thin, fan-like plate extending posterior to the genital segments. It
overhangs the anus and genital pouch, which will be described shortly. In P.
americana tergite 10 is cleft
posteriorly (Fig 10).
Figure 13. Ventral
view of the posterior end of the abdomen of a female of P.
at the ventral surface of the abdomen (Fig 13). Sternites 8 and 9 cannot be seen
7 (= hypogynum) is much larger and more heavily sclerotized than other sternites
and posses a pair of clamshell-like posterior valves, the subgenital plates
(also referred to variously as sternites 7 ¢ or
at first the plates may appear to be independent of sternite 7, they are in fact
continuous with it and connected by a short isthmus (Fig 13, 14). The
isthmus is flexible and the plates can move apart during copulation or to permit
extrusion of the ootheca as it is formed.
the specimen upright and focus on the posterior end. This
is much easier if you first separate the posterior abdomen from the remainder of
the body (Do not remove the posterior abdomen if you plan to use this specimen
later for study of internal anatomy). Make
the separation between segment 6 and 7. You
can now stand the posterior abdomen upright on the wax of the dissecting pan and
you will not have to hold it in position. Focus
on the posterior end of the abdomen (Fig 14).
Figure 14. Posterior view of the abdomen of a female P.
fuliginosa. Arrows indicate movement of the subgenital plates. Blatt50L.gif
7-10 dorsally and sternite 7 ventrally enclose a large space. The
space is divided into dorsal and ventral regions by two lateral sclerites, the paraprocts (Fig
14, 21-11B). The anus opens into the dorsal chamber whereas the oviduct and
seminal receptacle open into the ventral chamber, which is the genital pouch
(Fig 15). With
forceps pull the paraprocts aside to reveal the anus on
segment 10-11 under the epiproct.
The genital pouch is formed by invagination of the
exoskeleton of the sternum which brings sternites 8 and 9 deep into the pouch
(Fig 15). This
is the reason you could not see these sternites externally. With
forceps and needles as needed, pull the subgenital plates of sternite 7
laterally and ventrally to reveal the genital
pouch (= gynatrium). The
genital pouch receives the spermatophore from the male during copulation and
later the ootheca is molded in it.
The most conspicuous feature in the genital pouch is the ovipositor (Fig
15). It is a median process arising from the roof of the genital pouch and
consists of three pairs of cuticularizedvalvulae (=
valvulae are derived from the paired appendages of segments 8 and 9. The
ovipositor guides eggs from the oviduct to the forming ootheca. The
male external genitalia grip the ovipositor during copulation.
Sternite 8 can
be seen by lifting the ovipositor dorsally and looking under it Fig 15, 23). Sternite
8 is a large sclerotized plate penetrated by the female
gonopore opening from the
common gonoduct. Sternite
9 is at the base of the
Figure 15. Sagittal section of the posterior abdomen
of a generalized female cockroach. S
= sternite, T = tergite. Redrawn from Cornwell (1968) after McKittrick (1964).
The dorsum of the male posterior abdomen is similar to that
of the female. Tergite
7 is large and tergites
8 and 9 are
much smaller and obscured by the overhang of 7 (Fig 16). Tergite
10 is a large, posteriorly
cleft plate fused with tergite 11 to form the epiproct.
Figure 16. Dorsal view of the posterior abdomen of P.
americana. T = tergite. Blatt52L.gif
The male venter is very different from that of females. Sternites
8, and 9 are
unremarkable and unmodified from the condition of the more anterior sternites
and visible externally (Fig 17). Sternite 9 is the posteriormost sternite and
its posterior border bears a slender stylus on
each side. Styli are absent in mature females but are present in nymphs of both
sexes (Fig 21-12B).
A pair of triangular paraprocts is
located immediately ventral to tergite 10-11 and lateral to the anus
(Fig 14). Between
the paraprocts and sternite 9 is a large genital
pouch in which are housed
the male external genitalia.
Figure 17. Ventral view of the posterior abdomen of a
male P. americana.
Anchor the posterior abdomen, ventral side up, with a pair of
pins passing through the lateral tergites of segment 7. Lift
or remove sternites 8 and 9 to reveal the genital pouch and its contents (Fig
18, 24). The
male external genitalia comprise the several complex sclerites and soft tissues
of three phallomeres (=
phallic lobes, = gonapophyses), surrounding the male gonopore. The phallomeres
are responsible for moving the subgenital plates aside to open the female’s
genital pouch and for holding the female genitalia during copulation. Muscles
arising on segment 9 extend to the phallomeres and operate them. Phallomeres are
the appendages of segment 9.
Viewed from the venter, the ventral
phallomere (Fig 18) is the
most obvious of the three and can be seen immediately under sternite 9 (which
has been removed or lifted). It
is ventral to the gonopore and is by far the simplest of the three lobes. Its
ventral surface is a slightly cupped sclerotized plate but it is membranous
dorsally. The membranous ejaculatory duct ends at the gonopore on the dorsal
surface of its base. Because
it bears the gonopore, it is sometimes known as the penis.
phallomere is left of the
ventral lobe and a little dorsal to it (Fig 18). It
is a complex structure consisting of many sclerotized pieces including a hooked
lobe (= grumolobus, titillator), prickly lobe (= acantholobus), a sharp stylet
(= acutolobus, asperate lobe), and a pseudopenis. These
are used during copulation to hold the valvulae of the female ovipositor so the
spermatophore can be deposited in the correct location (at the opening of the
Figure 18. Ventral view of the posterior abdominal
segments of a male P. americana.
Sternites 8-9 have been removed and the phallomeres rearranged slightly for
clarity. Some membranes
and connective tissue have been removed. S
= sternite, T = tergite. Blatt54L.gif
phallomere is to the right
of the ventral phallomere and gonopore and is farther dorsal than either of the
other two lobes. It is less complicated than the left lobe but also has easily
recognized sclerotized parts. These
include a piece that looks like a crayfish cheliped (= dikella, serrate lobe)
and slender hooked piece (= falx).
cricket, Acheta, is
recommended as an alternative for the study of internal anatomy in preference to
the cockroach. Even
though it is smaller, it is easier to dissect and its internal structures are
easier to demonstrate.
the study of cockroach internal anatomy with a fresh, undamaged specimen if
dissection will be made from the dorsal side so you must first remove the wings
by cutting their attachments with a pair of fine scissors. The dissection is
facilitated if the legs are removed by cutting across their trochanters. Organ
systems will be considered in order of their appearance in dorsal dissection.
the specimen in a small dissecting pan of water or alcohol so it is completely
immersed. Insert the blade of a pair of fine scissors under the posterior
overhang of the right side of tergite 7 about 1 mm from the lateral margin of
the tergite. Insert
the blade only as deep as is necessary to penetrate the exoskeleton and be
careful you do not damage internal organs with deep cuts. Cut anteriorly along
the right side of the tergites all the way to the anterior end of the pronotum
(Fig 19). Cut
transversely across the anterior margin of the pronotum, just posterior to the
head, and upon reaching the left side, change directions and cut posteriorly
along the left side all the way back to tergite 7. Make
a transverse cut through the exoskeleton across the posterior border of tergite
7. You have now cut all of the way around the dorsum.
Figure 19. Dorsal view of a male P.
nota and abdominal terga 1-7 have been removed. T = tergite. Blatt55L.gif
the specimen to the wax of the dissecting pan with a #1 stainless steel insect
pin through the left side of one of the thoracic segments, lateral to your
the pin at a 45 ° angle. Remove
the abdominal and thoracic tergites beginning with tergite 7. Lift
each tergite and remove it without removing any of the underlying soft tissues. The
tergites are transparent and thin whereas the underlying tissues are opaque.
These tissues include muscles, heart, and tracheae. Do
not remove the opaque tissue at this time.
the abdomen the tergal
muscles form a broad thin
sheet of longitudinal muscle fibers (Fig 19). In
the thorax the tergal muscles are smaller and confined by other muscles, chiefly
those operating the legs. Running along the midline of this muscle layer is the
you accidentally remove the muscle layer, the heart will be destroyed, so be
system is the first organ
system uncovered in dorsal dissection (Fig 19). It
consists of the hemocoel, blood, and heart. The
hemocoel is divided by perforated horizontal membranes, known as diaphragms,
into a shallow dorsal pericardial sinus, a spacious perivisceral sinus, and a
small ventral perineural sinus (Fig 16-7). Together the sinuses form a large
partitioned blood space, the hemocoel. The hemocoel is the functional body
cavity of these acoelomate animals.
heart, surrounded by the pericardial sinus (= pericardial hemocoel) lies
immediately under the tergites. Removal
of the tergites opens the shallow pericardial
sinus, although it is not at all obvious that you are looking at a
blood space. It
is the space between the exoskeleton and the dorsal diaphragm. The
perforated, horizontal dorsal
diaphragm is the sheet of
connective tissue with longitudinal tergal
muscles on top of it (Fig
diaphragm separates the pericardial sinus from the much larger perivisceral
two sinuses are part of the hemocoel. Blood on its way back to the heart flows
through the perforations in the diaphragm.
The heart is
a longitudinal middorsal tube extending the length of the body in the
pericardial sinus and resting on the dorsal diaphragm (Fig 19). The
heart has segmental swellings, paired segmental ostia, paired segmental arteries
(unusual in insects), and paired segmental alary muscles. The
ostia, segmental vessels, and muscles will not be seen and most of the swellings
are inconspicuous. The
heart opens anteriorly into the cephalic hemocoel of the head and posteriorly
bifurcates to form two arteries.
arthropods blood is pumped anteriorly, during systole, by contractions of
circular muscles in the heart wall. Blood leaves the heart, enters the cephalic
hemocoel and passes posteriorly through the three sinuses of the hemocoel,
eventually passing through the perforations of the diaphragms to enter the
pericardial sinus. During
diastole contractions of radiating alary muscles cause the heart to dilate and
draw blood into its lumen through the ostia. The heart is now refilled with
blood and ready to enter another systole. Heartbeat
reversal has been observed in cockroaches.
respiratory system consists of 10 pairs of spiracles which open into a complex
system of distributory tracheae which deliver oxygen to the tissues. In
insects the blood is not involved in oxygen transport.
of the tergites exposes the network of branching, tubular, white or silvery tracheae (Fig
fine forceps to remove muscles and connective tissue covering some of the
tracheae and spiracles to improve your view of them.
tracheae arise at spiracles (Fig
12, 19) in the pleura near the posterolateral corners of the tergites and join
with other tracheae to form a single network of air tubes for the delivery of
oxygen to the tissues (Fig 21-10B, C). Two pairs of spiracles are present in the
thorax and eight pairs in the abdomen. No spiracles are present in the head. The
spiracles were seen earlier in your study of the external anatomy.
each side the respiratory system includes three longitudinal trunks and
segmental tracheae to the three hemocoel sinuses and their viscera. The portion
of the system you see at present consists, on each side, of a lateral
longitudinal trunk extending
from spiracle to spiracle (Fig 19), a series of dorsal
segmental tracheae extending
from the spiracles to the heart and pericardial sinus, and a dorsal
longitudinal trunk connecting
the dorsal segmental tracheae medially. The dorsal longitudinal trunks lie
beside the heart. Other
segmental vessels, which cannot be seen at present.
> 1a. Remove
a short piece of trachea and make a wetmount with it. Examine
it with the compound microscope at 100X and 400X with the light carefully
the closely spaced rings of chitin, similar in function to the cartilaginous
rings in a vertebrate trachea. These rings, known as taenidia,
hold the tracheae open, permitting air to pass unimpeded (Fig 21-10A). The
taenidia is actually a single helix of chitin, not a series of rings at all. The
helix has a very short wavelength so its coils are adjacent to each other, like
a Slinky™ at rest. <
you remove tracheae from the thorax some taenidia may uncoil and extend as a
long, tough, very fine thread, thus demonstrating that it is a continuous coil,
not a series of separate rings.
the dorsal diaphragm along with the tergal muscles, tracheae, and heart from the
this by cutting with fine scissors around the periphery of the abdomen. Be
very careful that you do not cut deeper than the diaphragm. The crop of the
digestive system is a large, thin walled chamber filling most of the abdomen. Its
walls may be closely appressed to the dorsal diaphragm, creating the risk that
it will be removed with the diaphragm. Remove the muscles, heart, and tracheae,
but nothing else, from the thorax. Be careful removing tissue in the thorax that
you do not inadvertently destroy the salivary glands and salivary reservoirs,
both of which are closely associated with the walls of the anterior gut
space you have uncovered is the large, spacious perivisceral
hemocoel, in which most of the viscera are found (Fig 16-7). Note
the large, amorphous, white fat
body in the hemocoel (Fig
22). This versatile tissue occupies much of the space in the abdominal hemocoel
but is also present in the thorax. It shares many functions with the vertebrate
liver and annelid chlorogogen. The
fat body functions in storage of lipid, glycogen and protein reserves. Stored
food in the fat body supports survival over long periods of starvation and its
size varies depending on the extent of starvation. It
is a site for intermediary metabolism, amino acid synthesis, blood glucose
regulation, vitamin synthesis, and uric acid storage. Some
of these functions are mediated by mutualistic, intracellular bacteria known as
the two pairs of large diameter tracheae extending through the thorax into the
pair lies beside the heart, the other is ventral, beside the esophagus. They
will be destroyed as you remove tissues to reveal the gut.
cockroach gut, like that of other arthropods, consists of an anterior,
ectodermal stomodeum, or foregut, a middle endodermal midgut, and a posterior
endodermal proctodeum, or hindgut. Both stomodeum and proctodeum, being
ectodermal, are lined by epidermis and exoskeleton, which in some regions may be
sclerotized. The foregut has chief responsibility for mechanical digestion,
trituration, chemical digestion, and storage, the midgut is the region of enzyme
secretion, chemical digestion and absorption. Water reclamation, feces formation
and storage occur in the hindgut. It
is also a storage kidney that sequesters uric acid.
foregut consists of mouth, pharynx, esophagus, crop, and proventriculus (Fig
21-8A, 16-9). The
midgut consists of midgut and digestive ceca. The
hindgut is composed of an ileum, colon, and rectum. The
ileum and colon together are sometimes known as the intestine.
mouth was seen earlier opening from the roof of the preoral cavity (Fig 21-7). It
opens onto the pharynx which extends dorsally through the head capsule. It
will not be seen from your present viewpoint. It becomes the esophagus and exits
the head capsule to enter the thorax, where it widens. The esophagus is
a conspicuous feature of the anterior thorax (Fig 20) where it can be recognized
as a ridged, thin-walled tube.
pair of white, multi-lobed salivary
glands and a pair of
bladder-like salivary reservoirs adhere to the walls of the esophagus (Fig 20). Saliva
is secreted by the glands and stored in the reservoirs. The salivary glands
extend posteriorly from mid- prothorax through the mesothorax. Salivary
glands and reservoirs are drained by ducts which extend anteriorly into the
head, eventually to coalesce and empty into the salivarium of the preoral
walls of the ducts are reinforced by helical rings similar to the taenidia of
tracheae. Here the saliva is mixed with food particles masticated by the
mandible and maxillary lacinia. The
saliva contains amylase.
Figure 20. Dorsal view of the perivisceral coelom of
a male P. americana. The
dorsal diaphragm, heart, and tergal muscles have been removed. Abdominal
segments are numbered. Malpighian
tubules have been shortened and reduced in number for clarity. Blatt56L.gif
the junction of the mesothorax and metathorax the esophagus widens to become the crop. This
thin-walled, expansible storage organ may fill the perivisceral hemocoel of the
posterior thorax and anterior abdomen. Its thin, transparent walls may push
against the body wall and dorsal diaphragm. The crop of preserved specimens may
contain a large air bubble. Almost
all hydrolysis occurs in the crop making use of enzymes from two sources. Salivary
amylase, is mixed with the food in the salivarium and then ingested, whereas
enzymes from the digestive ceca, move anteriorly from the midgut.
the vicinity of segments 5-6 the crop narrows to become the short, muscular,
thick-walled proventriculus (=
region of the foregut has cuticularized walls with heavily sclerotized, black or
golden brown teeth (Fig 21, 21-8B). These
may be faintly visible through the walls of the crop but the walls of the
proventriculus are opaque and you will get a better look later when you open the
gut. Esophagus, crop, and proventriculus are regions of the foregut.
gut narrows abruptly posterior to the proventriculus and becomes the midgut (=
transition from foregut to midgut is marked internally by the stomodeal valve,
that protrudes into the anterior midgut (Fig 21).
whorl of eight long, fingerlike diverticula, the digestive
ceca, marks the beginning of the midgut (Fig 20, 21-8A). The
ceca increase the surface area for secretion of enzymes and absorption of
produced in the ceca include invertase, lipase, maltase, protease, (and perhaps
cellulase in some species). Lactase is also present in the midgut. Some of these
may be produced by symbiotic gut microorganisms and it may be that amylase is
the only digestive enzyme produced by the roach itself.
midgut makes an asymmetric loop, curving to the right, then bending sharply
anteriorly, and then ventrally before heading posteriorly and dorsally. Immediately
after resuming its position on the midline it becomes the ileum of the hindgut.
transition from midgut to hindgut is marked by 60-150 long, slender, white,
threadlike, blind-ending Malpighian
tubules in six clusters (Fig
21-8A, 21-9). The
tubules are hollow gut diverticula that extend into the hemocoel where they are
bathed in blood. In Periplaneta they
contain intracellular enzymes and may be more important in digestion than in
first region of the hindgut is
the short, narrow, muscular ileum.
It extends for a short distance posteriorly from the midgut and then dilates to
become the colon.
The transition is marked internally by the ileocolic valve, a sphincter muscle. The
colon extends posteriorly to about segment 7 where it expands to become the rectum. The
wall of the rectum bears six longitudinal, opaque, white ridges, the rectal
pads protrude into the lumen of the rectum where they remove water from the
forming feces. The
rectum efficiently reclaims water from feces when water is scarce and
conservation is advantageous, producing dry hard fecal pellets. When
water is abundant, however, the rectum does not remove water so effectively and
produces wet fecal pellets. Insect
fecal pellets have characteristic patterns of longitudinal grooves and ridges
impressed on them by the rectal pads.
rectum ends at the anus,
under tergite 10 between the two paraprocts. Slip a needle under tergite 10
between the paraprocts and watch it appear in the rectum.
fine scissors to open the posterior crop and proventriculus. Inside
the proventriculus you will find an elaborate gastric
mill composed of an
assortment of sclerotized plates (Fig 21, 21-8A,B). Three
sets of six plates each are embedded in the proventricular wall. In
a circle adjacent to the crop are 12 plates in two alternating sets. Six
are toothed plates,
each with a large complex tooth, and six are ridged
plates, each with several parallel ridges. The teeth continue the
mechanical breakdown of food particles initiated by the mandibles and maxillae.
Six additional plates are arranged in a second whorl, this one closer to the
lightly sclerotized plates support soft cushions, the pulvilli,
bearing short fine setae which presumably act as a filter to exclude large
particles from the midgut. The astonishing gastric mill of the insect
proventriculus is a sight you don’t want to miss.
the incision along the midgut and hindgut noting that these regions are lined by
a loose transparent peritrophic
membrane (Fig 21-9). If
food is present in the gut of your specimen, it will be contained within the
peritrophic membrane. The
membrane is secreted continuously by the gut epithelium.
Figure 21. Interior of the proventriculus.
may employ several mechanisms for eliminating or inactivating nitrogenous waste
products, chiefly as uric acid. It is not known which is most important.
nitrogen may be transferred from the blood to the gut lumen, and thus to the
feces, by Malpighian tubules and the midgut. In most insects the Malpighian
tubules remove wastes and
inorganic ions from the blood and secrete them into the gut lumen, where they
become incorporated in the feces and are eliminated. Uric acid has not been
demonstrated in cockroach Malpighian tubules, however, and it may be that, since
they are known to contain digestive enzymes, their role is in digestion rather
of the functions of the fat
body is the sequestration,
storage, and possibly recycling of nitrogenous waste products. Specialized
urate cells in the fat body synthesize uric acid from waste nitrogen and store
it indefinitely. Cockroaches
on high protein diets develop a hypertrophied fat body functioning as a storage
is thought that endosymbiotic prokaryotic cells (bacterioids) use the stored
nitrogen for protein synthesis. Storage in the fat body is probably the most
important excretory mechanism in cockroaches.
males of a few cockroach species nitrogen is excreted by the accessory glands of
the reproductive system. Some
tubules of this gland absorb and store uric acid which is then deposited in the
spermatophore and eliminated during copulation. This mechanism, of course, is of
no use to females and is limited to males of only a few species (such as Blatella
germanicabut not Periplaneta).
periodic molting by arthropods is potentially a mechanism for eliminating
unwanted materials from the body. It has been suggested that the nitrogen, as
protein, incorporated in the developing cuticle during can serve as a mechanism
for eliminating excess nitrogen. The
incorporated nitrogen is then jettisoned with the next molt. This
mechanism could be effective in nymphs but not adults, since they do not molt.
female internal genitalia consist chiefly of a pair of ovaries, two colleterial
glands (= female accessory glands) with separate ducts, seminal receptacle (two
in some species), and oviducts (Fig 21-11A). Each ovary is a bundle of tapering
tubes, the ovarioles, which empty into an oviduct. Oogenesis
and gamete maturation occur in the ovarioles. The
lateral oviducts, one from each of the two ovaries, join to form a common
oviduct that opens through sternite 8 into the genital pouch (Fig 15). The
duct from the seminal receptacle opens at the end of the receptacle papilla in
the pouch (Fig 23). During
copulation the male attaches a spermatophore a sternite in the female genital
exit the spermatophore, travel up the receptacle duct to the seminal receptacle
where they are stored, potentially for a year or more.
female reproductive system will not be visible until much of the fat
body in the dorsal abdomen
has been removed. Begin
first in the posterior abdomen and remove tergites 7-9 if you have not already
done so. The fat body covers and is packed around the colleterial glands and
ovaries and must be removed carefully without damaging either. The
size of the fat body varies depending on metabolic and reproductive condition of
the insect. Reserves
stored in the fat body are transferred to the developing eggs when the female is
you have removed the fat body, the left colleterial
gland will be conspicuous as
spaghetti-like tangle of many long, slender, branching, opaque
white tubes. The
glands lie beside and dorsal to the hindgut and, along with the fat body,
obscure your view of everything else in the posterior abdomen (Fig 22). The
colleterial gland is not restricted to the surface and fills much of the space
between the sternum and tergum. The smaller right colleterial gland will
probably not be seen.
two colleterial glands empty via separate ducts into the genital pouch. The
two glands differ dramatically both morphologically and chemically. The left
gland is much larger than the right and completely obscures it from view.
Secretions from both are released simultaneously into the genital pouch and
react to form the sclerotized lining of the pouch that will become the ootheca. Protein
released from the left gland is tanned by phenol from the right gland. The
resulting wall of the ootheca wall is composed of scleroprotein identical to
that in cuticular sclerites, although chitin is absent. Eggs are deposited into
this lining as they leave the ovarioles and the lining then hardens (tans) to
become the ootheca.
The ovaries lie
laterally in the abdomen, one on either side of the gut and may extend for most
of the length of the abdomen. Or, if immature or inactive, may be restricted to
abdominal segments 5-7. The ovaries are hidden from view by the fat body and
colleterial glands, which much be removed.
ovary is a bundle of large tapering tubes, the ovarioles.
In Periplaneta each
ovary consists of eight ovarioles (Fig 22). Each
ovariole is a connective tissue tube consisting of two regions. The germarium is
the short, small-diameter, upstream, anterior region. Oogonia in the germarium
initiate oogenesis culminating downstream in the production of oocytes. Thevitellarium is
the much longer, much wider, downstream region in which follicle cells transfer
nutriment to the maturing and growing oocytes. The diameter of the ovariole is
very small in the germarium but increases downstream as the developing gametes
accumulate yolk from the follicle cells and increase dramatically in size (Fig
Figure 22. Dorsal view of the opened abdomen of a
female P. fuliginosa. The
fat body and colleterial gland have been removed from the left side to reveal
the left ovary. T = tergite. Blatt58L.gif
downstream ends of the eight ovarioles of each ovary coalesce to form a lateral
oviduct (Fig 21-11A). Remove
the colleterial glands from one side and find the lateral
oviductexiting the large, posterior, basal end of the ovary. Upon
exiting the ovary the oviduct passes deep into the tissues in the ventral
abdomen and extends medially to join the other oviduct on the ventral midline. The
junction of the right and left lateral oviducts forms the short unpaired common
oviduct which passes
posteriorly to open through the female gonopore in the genital pouch (Fig 15,
gametes are lined up one after another in the ovariole with oocytes maturing as
they move downstream (Fig 22). The
mature egg (actually, it is a secondary oocyte that will not complete meiosis
until it is fertilized) is the downstream-most gamete in the ovariole. Each
ovariole typically has a single mature egg ready for fertilization and
incorporation into an ootheca (Fig 22). Eggs
leave the ovarioles via the oviduct and are fertilized by sperm from the seminal
receptacle as they enter the genital pouch. The
ovipositor manipulates them and orients them properly in the developing ootheca.
If the eggs are mis-oriented, the nymphs will be unable to escape from the
ootheca and will die . The ootheca hardens around two rows of eight eggs each,
one from each of the 16 ovarioles (eight ovarioles in each of two ovaries). The
number of eggs in the ootheca depends on the number of ovarioles in the ovary
and differs with species.
of some species (e.g. Blatella
germanica) retain the ootheca and brood their eggs. Most,
including Periplaneta, drop
the completed ootheca and abandon it.
Figure 23. Dorsal view of the floor of the genital
pouch with the gut, fat body, and colleterial glands removed. Blatt59L.gif
male reproductive system consists of paired testes, each draining by a sperm
duct (= vas deferens) to a common ejaculatory duct which opens via the male
gonopore in the genital pouch (Fig 21-12A). Associated
with the confluence of the two sperm ducts are two clusters of secretory
accessory glands. Near
the confluence, the sperm ducts are expanded to form seminal vesicles. It is
thought that spermatogenesis occurs in the testes during the last nymphal instar
and the spermatozoa stored for later use as an imago.
testes are located dorsolaterally in segments 4 and 5 (Fig 20). They
are embedded in the white fat body and can be difficult or impossible to
demonstrate in adults, especially older specimens. Part of this difficulty is
attributed to the alleged (disputed) degeneration of the testes in older adults
but most of the problem is due to the fat bodies. Like the testes, the sperm
ducts are difficult to demonstrate and you probably will not see them.
to copulation a spermatophore is formed in the male ejaculatory duct when
secretions of the accessory glands enclose and harden around a mass of sperm
from the seminal vesicles. During copulation the phallomeres open the female’s
genital pouch and hold the male’s genitalia in the correct position. The
ejaculatory duct on the ventral phallomere is held adjacent to the opening of
the spermathecal papilla (Fig 23) and the spermatophore released. It is believed
that the spermatophore is glued in place by secretions of the male’s phallic
gland. In about 24 hours or less, sperm exit the spermatophore and are stored in
the female’s seminal receptacle.
Figure 24. Dorsal dissection of the posterior
hemocoel and genital pouch of a male P.
americana. The internal
genitalia (accessory glands) have been removed. Blatt60L.gif
dorsal dissection your view of the male reproductive system is probably obscured
by lobes of the bright white fat body. Remove
this region of the fat body and tergite 8-9 if you have not already done so.
removal of the fat body, the male accessory
gland (= mushroom gland) is
by far the most conspicuous of the male's internal genitalia (Fig 20). It
secretes the covering of the spermatophore and is a mass of worm-like
diverticula in the posterior hemocoel under tergites 7-8 beside the anterior end
of the posterior colon and anterior rectum. The
mass includes large (utriculi majores) and small (utriculi breviores)
diverticula and is usually surrounded by lobes of the fat body.
two sperm ducts enter the gland and the seminal vesicles are enclosed in the
mass of tubules. The thick ejaculatory
duct, formed by the union of the sperm ducts, exits ventrally from the
center mass of accessory glands and extends deep into the ventral body wall and
then posteriorly to the gonopore on the dorsal surface of the ventral phallomere
of the phallic gland is
ventral to the nerve cord and should not be exposed until you have completed
your study of the nervous system (Fig 24). It
is deeply ventral in the posterior abdominal cavity, ventral even to the ventral
diaphragm and is a little to the right of the midline. Remove
the tissue ventral to the posterior nerve cord to expose the gland. Its
appearance is distinctive. It
is glandular, white, and shaped like an elongate teardrop, tapering posteriorly
to form the phallic gland
duct. It is between abdominal ganglion 5 and the terminal ganglion. It
is ventral to the terminal ganglion and the right cercal nerve. Its duct opens
in the genital pouch between the pseudopenis and acutolobus of the left
phallomere (Fig 18, 24). During
copulation secretions of the phallic gland are used to attach the spermatophore
in the vicinity of the opening of the seminal receptacle.
basic features of the insect nervous system are the dorsal brain joined by
circumenteric connectives to ventral nerve cord with paired segmental ganglia.
It includes both somatic and visceral components and is served by a variety of
sensory devices. Most,
but not all, segments have a pair of segmental ganglia. Segmental ganglia and
the brain consist of paired lateral ganglia connected by a transverse
cockroaches the commissures are short resulting in fusion of the lateral ganglia
so each segmental ganglion seems to be a single ganglion.
the gut, ventral diaphragm, and muscles from the thorax and abdomen. Remove
the longitudinal body wall muscles (sternal muscles) and connective tissue as
necessary from the floor of the abdominal cavity to reveal the ventral
nerve cord (Fig 16-11). The
cord consists to two side-by side, parallel, longitudinal connectives which are
united by transverse commissures passing between paired segmental
ganglia. Notice the longitudinal
ventral tracheal trunk lying
beside the ventral nerve cord.
ganglia are located in the
thorax (Fig 25). From
each extends several pairs of nerves to the abundant muscles of these segments. These
are large ganglia.
Figure 25. Dorsal dissection of P.
americana. T = thoracic ganglion, A = abdominal ganglion. The
abdominal segments are numbered. Blatt61L.gif
the abdomen are six much smaller abdominal
ganglia. Abdominal ganglia 1-3 are scarcely wider than the double nerve
cord and can be difficult to distinguish from the cord. Abdominal
ganglia 4 and 5 are usually readily discernable. The
sixth abdominal ganglion, known as the terminal
ganglion, is the largest of the abdominal ganglia and is easily
recognized. The nerve cord ends at the terminal ganglion which gives rise to two
large sensory cercal nerves to
the cerci. The
terminal ganglion is the coalesced ganglia of several posterior segmental
your finest scissors and forceps carefully remove the epicranium from the region
between the compound eyes and antennae. Remove
muscles as necessary to reveal the bright white, dorsal brain between
the compound eyes (Fig 25). The brain consists of two cerebral
ganglia fused across the
midline. Short thick optic nerves extend
from the eyes to the brain. Smaller antennal
nerves run from the antennae
to the brain. Remove
the mandibles and other tissues from one side of the head to reveal the thick circumesophageal
connectives.These exit the ventral side of the brain and extend
posteriorly to pass around the esophagus, and then coalesce to form the subesophageal
ganglion ventral to the gut. Nerves
to the mandibles, maxillae, and labium exit the subesophageal ganglion. A pair
of longitudinal nerve cords exit the subesophageal ganglion as the ventral nerve
cord and pass posteriorly through the foramen magnum to thoracic ganglion 1 (Fig
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keys, arthropods, reptiles, birds, and mammals of public health significance. US
Public Health Service, Communicable Disease Center, Atlanta. 192 pp.
Barbara KA .
University of Florida Institute of Food and Agricultural Sciences, Periplaneta
americana page: http://creatures.ifas.ufl.edu/urban/roaches/american_cockroach.htm
Bell WJ, Adiyodi KG. 1981. The
American cockroach. Chapman and Hall, London.
Borror DJ, Triplehorn
CA, Johnson NF. 1986.
An introduction to the study of insects. Saunders, Philadelphia. 875pp.
Buck JB, Keister ML. 1950. Periplaneta
americana, pp475-496 in Brown FA (ed), Selected invertebrate types. Wiley,
New York. 596pp.
Cornwell PB. 1968.
The cockroach, vol 1, A laboratory insect and industrial pest. Hutchinson of
Ebling W. 1975.
Urban entomology. Univ. Calif, Richmond CA.
Furman DP, Catta EP. 1970.
Manual of medical entomology, 3 rd ed.
National Press Books, Palo Alto. 163 pp.
Guthrie DM, Tindall
The biology of the cockroach. Edward Arnold Publisher. 408pp.
McKittrick FA. 1964.
Evolutionary studies of cockroaches. Cornell Univ. Agric. Expt. Sta. Mem. 389.
Miall LC, Denny A. 1886.
The structure and life history of the cockroach. Lovell Reed Company, London.
Ruppert EE, Fox RS,
Barnes RB. 2004.
Invertebrate Zoology, A functional evolutionary approach, 7 th ed.
Brooks Cole Thomson, Belmont CA. 963 pp.
Snodgrass RE. 1935.
Principles of insect morphology. McGraw-Hill, New York. 667pp.
LA. University of Florida Institute of Food and Agricultural Sciences, Evania
Living or preserved adult cockroach, preferably Periplaneta
Dissecting equipment with microdissecting forceps
Small dissecting pan made from anchovy or sardine can with
dissecting wax bottom.
Anesthetic (chloroform, ether, or carbon dioxide) or
Killing agent (ethyl acetate)
# 1 stainless steel insect pins