Download thorax abdomen

External Anatomy – Thorax and Abdomen
Objectives of the lab:
1. Define and use the vocabulary, particularly all terminology in bold.
2. Examine and identify thoracic and abdominal segmentation and observe modification
(female and male external genitalia, stingers etc.)
3. Determine the gender of the insects
4. Identify general wing structure and discuss wing modification
5. Diagram and identify the parts of typical insect legs and observe leg modifications
according to lifestyle
1. External examination of the lubber grasshopper, Romalea microptera
Examine a male or female Romalea under magnification (using either the dissecting microscope
or the magnifying glasses provided). The arthropod body is composed of a linear series of
segments, some or all of which bear paired jointed segmental appendages. Most arthropods,
including insects, are heteronomous, with their segments and their appendages variously
modified and grouped in regions, or tagmata, specialized for different functions. The alternative
homonomous condition, with all segments and appendages alike over the length of the body, is
primitive and among recent tax only apparent in some crustaceans. The three tagmata of the
insect body are the anterior head, middle thorax, and posterior abdomen. The head, which shows
few external signs of segmentation, bears the eyes, antennae, mouth, and mouthparts. Its major
functions are sensory reception and feeding. The thorax, whose primary function is locomotion,
is larger and bears three pairs of legs and, typically, two pairs of wings. The abdomen is the
largest tagma and is conspicuously segmented. It houses most of the digestive, excretory, and
reproductive viscera and its appendages, when present, are specialized for copulation or
oviposition. Most abdominal segments lack appendages and those present are highly modified.
The external genitalia, at the posterior end of the abdomen, are highly modified segmental
appendages.
Thorax
The heavily sclerotized head and thorax are connected by a short narrow neck, or cervix, whose
integument is lightly sclerotized and consequently soft and flexible. The neck and its leathery
integument are easiest to see ventrally but are hidden dorsally by the head and thorax. A few
hard, sclerotized plates, the cervical sclerites, are embedded in its integument.
The insect thorax consists of three segments, each of which bears a pair of legs. The legs are
segmental appendages. Two of the thoracic segments may bear paired wings, which are complex
folds of the body wall not segmental appendages. The three thoracic segments are, in order from
anterior to posterior, the prothorax, mesothorax, and metathorax. The meso- and metathoraces
are fused rigidly to form an inflexible box housing the flight muscles and bearing the two pairs
of wings. Together they are referred to as the pterothorax in reference to the wings they bear
(pter = wing). The prothorax is joined to the pterothorax and to the head by flexible articulations.
A typical arthropod segment is enclosed in four exoskeletal plates, or sclerites, that form a ring
around the segment. These are the dorsal tergite (notum), ventral sternite, and two lateral
pleurites. These sclerites are typically joined together by flexible articulating membranes but
sometimes they are fused rigidly together.
Prothorax: The grasshopper prothorax is covered by an unusually large shieldlike tergal plate
called the pronotum. The pronotum covers the prothorax and partly overhangs the mesothorax.
The prosternite, located ventrally, is much smaller and bears a conspicuous median prosternal
spine, by which may be recognized. The forelegs, or prothoracic legs, articulate with the
prothorax. The pleurites of the prothorax, known as propleurites, are small and located between
the prosternite and the pronotum. They are fused with both the prosternite and the pronotum.
Together the prosternite and propleurites form sockets for the articulation of the forelegs. The
propleurite forms the dorsal edge of the socket whereas the prosternite forms the ventral edge.
Note the flexible, unsclerotized cuticle forming an articular membrane between the base of the
leg and the socket. Rotate the leg around the articulation to demonstrate its mobility. Primitively,
each body segment bears a pair of lateral openings, or spiracles, for the intake of air into the
tracheal respiratory system. One such spiracle is found on each side of the prothorax. It is located
laterally near the border between the prothorax and mesothorax in the soft unsclerotized cuticle
under the posterior edge of the pronotum. The prothoracic spiracles are difficult to see because
they are hidden by the pronotum. The more posterior spiracles are easier to locate.
Pterothorax: The pterothorax comprises the mesothorax and metathorax. Each segment bears a
pair of wings and a pair of legs. The wings of the mesothorax are the forewings, or wing covers,
and those of the metathorax are the hindwings. The mesothorax bears the middle legs, or
mesothoracic legs. The metathorax bears the hindlegs, or metathoracic legs. Dorsally the two
segments of the pterothorax are covered by the two sclerotized tergites known as the mesonotum
and metanotum. Similarly the ventral surfaces are protected by the mesosternite and
metasternite. Note the manner in which sternites join together along their lines of fusion. The
metasternite is dovetailed into the mesosternite. The sternite of the first abdominal segment
resembles the thoracic sternites and is dovetailed into the posterior edge of the metasternite.
Deep invaginations at the corners of the dovetails are apophyseal pits marking the position of
important sternal apophyses, or apodemes, extending from the exoskeleton into the interior of the
pterothorax to function as an endoskeleton. The sides of the pterothorax are composed of
sclerites derived from the pleura of ancient insects. The pleurite on each side of both
pterothoracic segments is divided into two smaller plates. The legs articulate between the ventral
edge of the pleurites and the sternites. The wings arise between the dorsal edge of the pleurites
and the nota (tergites). A spiracle is situated laterally between the pleura of the metathorax and
mesothorax. Note that its opening is guarded by two movable lips, or valves. The opening is a
straight slit between the two lips. The spiracle opens into the tracheal system.
Legs
Study one of the middle legs. This appendage, which is typical of insect legs, is composed of a
linear series of units, or articles. Each article consists of a sclerotized exoskeletal cylinder
which contains muscles, tendons, blood, connective tissue, and nerves. Note that while most of
the limb exoskeleton is rigid and heavily sclerotized, some parts are flexible and unsclerotized.
The unsclerotized regions are the movable articulations between successive articles. Look at
some of the articulations under magnification and find these flexible articular membranes. The
first (proximal) article is the leg is the coxa (leg base). It is short, wide at the base, narrow
distally, and articulates by a broad articulating membrane with the socket formed by the pleurite
and sternite of the mesothorax. Articulated with the distal end of the coxa is the even shorter,
cylindrical trochanter. The trochanter is fused immovably with the long femur. The femur is
one of the two long articles of the leg. The tibia, which is the second of the long articles,
articulates with the distal end of the femur. Pay particular attention to the hard parts of the
articulation between the femur and tibia. They form a dicondylic hinge joint similar to that in
your elbow and knee (but exoskeletal rather than endoskeletal, of course). Such a joint restricts
motion to a single plane. You encountered another dicondylic joint between the mandible and
epicranium. The tibia is long and slender with teeth on its margins. Next in line along the length
of the leg is the tarsus composed of two subdivisions, or tarsomeres. The number of tarsomeres
varies among insects. The proximal tarsomere bears three soft, unsclerotized friction pads on its
surface to prevent slipping of the tarsus on the substratum. The distal tarsomere is much shorter
and has a single friction pad. The final article of the leg is the pretarsus. It extends from the
distal end of the tarsus and bears a pair of sclerotized tarsal claws and a single soft friction pad
(ariolum). The forelegs are nearly identical to the midlegs but the hindlegs are much large and
responsible for the characteristic jumping (saltational) locomotion of grasshoppers. The large
coxa of the hind leg is fused with the trochanter and the femur and tibia are much elongated. In
addition, the femur is expanded proximally to accommodate the major jumping muscles. This
expansion gives it a club or drumstick shape.
Wings
The two pairs of wings are evaginations or folds of the cuticle and body wall of the two segments
of the pterothorax. Each wing is a double layer of body wall consisting largely of cuticle but
underlain and secreted by epidermis. The characteristic wing veins of the wings are thickened
tubes of exoskeleton involved in support. Their primary function is structural but they contain
epidermis (which secretes the cuticle), nerves, and blood. Wing veins are divided into
longitudinal veins that that extend throughout the length of the wing and cross-veins that connect
the longitudinal veins. The longitudinal veins are:
Costa (C)
Subcosta (Sc)
Radius (R)
Cubitus (Cu)
Media (M)
Radial sector (Rs)
Media anterior (Ma) Anal veins (A)
Media posterior (Mp)
The cross veins connecting to the longitudinal veins are:
Humeral (h)
Radial (r)
sectorial (s)
Radio-medial (r-m)
Medial (m)
medio-cubital (m-cu) cubito-anal (cu-a)
The forewings of all grasshoppers, including Romalea, are heavy and form a pair of wing covers
to protect the more delicate hindwings. Those grasshoppers capable of flight use the hindwings,
and not the forewings, for flying. Lift and spread the wing covers (forewings) and examine them
with magnification. Note the heavy longitudinal veins and the abundance of small, branching
and anastomosing veins arising from them. Make a similar examination of the hindwings.
Abdomen
The grasshopper abdomen consists of 11 segments and extends posteriorly from the thorax. It is
the largest of the tagmata and most of its segments have no appendages. Its segmentation is
obvious externally, moreso than that of the other tagmata, and more like that of the ancestral
arthropods. With the exception of those at the posterior end, grasshopper abdominal segments
are easily recognized and counted. Numbered from anterior to posterior, abdominal segments 1-7
are similar to each other and are typical, unspecialized insect segments. These are the pregenital
segments and none bears appendages. Segments 8-9 are reduced and modified and may bear
appendages. These are the genital segments and may have appendages modified as external
genitalia. The gonopore is on segment 8 but it is hidden by the genitalia. Segments 10-11 are the
postgenital segments. Typically each segment is covered by a large dorsal tergite and a ventral
sternite. The two articulate laterally via a flexible, narrow articular membrane. Abdominal
sclerites are not as heavily sclerotized as are those of the thorax and head. Eleven tergites are
present but some of the posterior segments lack sternites and, as a consequence, there are only
eight sternites in females and nine in males. The pleurites are reduced and fused to the ventral
edges of the tergites. Most abdominal segments are similar to each other but the anterior and
posterior ones show some specializations. The first abdominal segment is fused rigidly with the
thorax. You have already seen its sternite dovetailed into the metasternite. Its tergite is mostly
hidden by the base of the hindwings. Each side of tergite 1 bears a large aperture covered by a
thin cuticular tympanic membrane (= tympanum or eardrum). These are auditory organs for
sound transduction. Some species of lubber grasshoppers have stridulating organs with which
they produce sound. The spiracle of the first abdominal segment is located on the anterior edge
of the tympanum. This spiracle opens into a large air sac attached to the inner surface of the
tympanum. Segments 2-7 are similar. The fifth abdominal segment is typical of the pregenital
segments. Its tergite forms a large arch over the dorsum and its sternite forms a broad band
across the belly. Both sclerites are joined to each other and with adjacent sternites and tergites by
flexible articular membranes. A spiracle is located at the extreme anterior ventral corner of the
tergite. The posterior abdominal segments are associated with the external genitalia and differ
from other segments and between males and females. Some bear modified segmental
appendages. The large anus is on segment 11 ventral to tergite 11 (tergite 11 is the epiproct). It is
covered dorsally by the single epiproct and flanked by two paraprocts. The ovipositor of females
and penis (= aedeagus) of males are ventral to the anus. The posterior abdomens of males and
females differ and must be studied independently. Exchange specimens with another student in
order to study the opposite sex.
Female
Externally, female segment 8 is similar to the preceding segments except that its sternite is
known as the genital plate. The egg guide is a triangular, median process of the genital plate.
Segments posterior to 8 are reduced and lack sternites. The tergites of segments 9 and 10 are
reduced and fused laterally although they remain separate dorsally. The 11 th tergite, or epiproct,
is rather large and it forms a triangular dorsal shield rather than an arch over the body. Its pointed
end projects posteriorly and covers the anus. Associated with it is a lateral paraproct on each
side, ventral to the epiproct. The paraprocts are probably the sternites of segment 11. Between
the 11 th tergite and each of the paraprocts is a small cercus. The cerci are the segmental
appendages of segment 11. In some orthopterans, such as crickets, they are long antenniform
sensory organs but in Romalea they are very short. The female external genitalia are modified
segmental appendages belonging to segments 8 and 9. Together they form the short robust
ovipositor extending posteriorly from the abdomen. The ovipositor consists of three pairs of
processes, called valvulae, which are used by the female to insert eggs into the ground.
Ventralmost is the pair of large, heavily sclerotized first valvulae (= ventral valves). Dorsally is
a similar pair of sclerotized third valvulae (= dorsal valves). The first and third valvulae are
conspicuous externally. The inconspicuous, membranous second valvulae (= inner valves) are
hidden from view by the first and third and will not be seen. The gonopore lies between the first
valvulae. The space enclosed by the epiproct, paraprocts, genital plate and ovipositor is the
genital chamber. The right and left first and third valvulae together form a hollow shaft, or
ovipositor, consisting of four parts, that is used to penetrate the soil. The eggs pass from the
gonopore, through the lumen of the shaft, assisted by the second valvulae, and are deposited in
masses in the soil. The first valvulae are derived from the appendages of segment 8 whereas the
second and third are the appendages of segment 9.
Male
The male posterior abdomen is simpler than that of the female. Segment 8 resembles segments 27 and has an unmodified sternite. Tergites 9-10 are fused ventrally and separate dorsally as in
females. Segment 9 possesses a large sternite, the subgenital plate that extends posteriorly
ventral to segments 10-11. It forms a cup enclosing the male external genitalia. Protected and
hidden by the plate is the soft (largely unsclerotized) eversible penis (= aedeagus). Although
referred to as “external” genitalia, the penis is not visible externally without moving the
paraprocts and subgenital plate aside. Segment 11 is similar to that of females and has a dorsal
tergite (= epiproct), lateral paraprocts, and short cerci. The anus is under the epiproct and
between the paraprocts. It can be seen by lifting the epiproct. The penis consists of a soft,
eversible, bulbous base bearing cuticularized valves, or claspers at its distal end. It contains an
extension of the ejaculatory duct through which spermatophores pass during copulation. The
gonopore is at the tip of the penis, between the claspers, but will not be seen. The penis lies in
the genital chamber. The genital chamber is the posterior space enclosed by the epiproct
dorsally, sternite 9 ventrally and the paraprocts laterally. Open it by pinning the posterior tip of
sternite 9 (subgenital plate) to the wax. Lift the epiproct and pin it. The space thus revealed is the
genital chamber. Its floor is occupied by a large, soft, eversible penis (= aedeagus), which is an
intromittent organ. Associated with the penis are dark, hard, sclerites. The male gonopore opens
on the midline at the tip of the penis and is flanked by two pairs of slender, dark, sclerotized
penis valves that hide it from view.
2. External examination of the cockroach, Periplaneta Americana
Species 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. The head is inconspicuous in dorsal view but the pronotum of the thorax is very
large. The remainder of the thorax and abdomen are hidden by the two pairs of wings. Six pairs
of similar, strong, spiny legs are present.
Thorax
The 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. 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 segment.
Legs
The 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. 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. 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. When flexed, the femur fits neatly into a recess in the surface
of the coxa. The articulations between coxa and trochanter and between femur and tibia are
dicondylic joints which restrict movement to a single plane. 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.
Wings
The 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. 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 pronotum. Use forceps and your fingers to extend the wings and examine
their shape and texture. Note the way in which the hindwing folds when at rest.
Thoracic Segments
The 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. The
ventral surface of the thorax consists of large expanses of unsclerotized, flexible, white
exoskeleton in which are embedded myriad hard, golden brown, sclerites. Anchor 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. On the midline, between the
right and left pleurites, lies a series of thoracic sternites. The prosternum 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.The 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. Consequently, the mesothoracic spiracle is
on the posterior prothorax and the metathoracic spiracle is in the membrane between the
mesothorax and metathorax. Study 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 uninitiated. It is heavily sclerotized and dark in color with a
pale border. The mesonotum is a transverse, lightly sclerotized plate covering the dorsal surface
of the mesothorax. The metanotum is similar and covers the mesothorax.
Abdomen
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 removed. The
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. Further, some of the segments, especially in
females, are highly modified or in unexpected locations and are not immediately visible and
countable. the 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. Dorsally each segment is covered by a sclerotized tergite and,
similarly, is covered ventrally by a sclerotized sternite. Consecutive sternites articulate with
each other by unsclerotized articular membranes. Laterally, tergites and sternites are connected
by unsclerotized flexible pleura.Examine the dorsum of the abdomen and find the abdominal
tergites. Those of segments 1-7 are similar in size and easily distinguished but tergite 8 is
smaller and tergite 9 smaller 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. Study the ventral surface of the abdomen. 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 abdomen. Sternites 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. Sternites 8, 9 are
internalized under tergite 7 and cannot be seen without dissection. 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 which are modifications of sternite 11. Sternite 10 is vestigial. Most abdominal
segments lack appendages but segment 10 bears a pair of large, segmented cerci, which are
visible in both dorsal and ventral views. 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.
Eight 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. 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.
Female
Study 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. 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. Look at the ventral surface of the abdomen (Fig 13).
Sternites 8 and 9 cannot be seen externally. Sternite 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 7a). Although 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. The isthmus is flexible and the plates can move apart during copulation or to
permit extrusion of the ootheca as it is formed. Hold 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. Tergites 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. The anus opens into the dorsal chamber whereas the oviduct and
seminal receptacle open into the ventral chamber, which is the genital pouch. 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. 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. It is a median process
arising from the roof of the genital pouch and consists of three pairs of cuticularized valvulae (=
gonapophyses). The 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. 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 ovipositor.
Male
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. Tergite 10 is a large,
posteriorly cleft plate fused with tergite 11 to form the epiproct. 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. 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.
A pair of triangular paraprocts is located immediately ventral to tergite 10-11 and lateral to the
anus. Between the paraprocts and sternite 9 is a large genital pouch in which are housed the
male external genitalia. 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. 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 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.
The left 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 seminal
receptacle). The right 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).
3. Examination of the different wing types
Please utilize the insects you collected during the first lab and some of the common insects on
the front table, familiarize yourself with different wing modifications and draw, describe and
label the different wing types.
1. Hemelytron – the half-sclerotized and half-membranous mesothoraic wing of true bugs
(Hemiptera). The metathoraic wing is entirely membranous.
2. Elytron – the sclerotized mesothoraic wing of beetles (Coleoptera).
3. Membranous – both pairs of wings are membranous for example in bees (Hymenoptera)
4. Haltere – the mesothoraic wings are membranous, metathoraic wings are modified into
halteres (small knobs on thin stalks) in flies (Diptera)
5. Tegmen – the leathery mesothoraic wing of grasshoppers and cockroaches (Orthoptera)
6. Scaled – both wings are covered in scales in butterflies and moths (Lepidoptera). You will
need to observe the wings of these animals under the dissecting microscope or using a
magnifying glass.
4. Examination of the different leg types
Please utilize the insects you collected during the first lab and some of the common insects on
the front table, familiarize yourself with different leg modifications and draw, describe and
label the different leg types. The leg types are dependent on the animals’ lifestyle which you
should consider during your examinations.
1. Cursorial (running)
2. Natatorial (swimming)
3. Fossorial (digging)
4. Raptorial (grasping)
5. Saltatorial (jumping)
5. Examination of abdominal structures
Examination of abdominal structures should include observation and drawing of the ovipostor
(females, particularly obvious in Orthoptera) and the stingers (Hymenoptera).