Shape, Size and Colour :
It’s body is dorso-ventrally flat, bilaterally symmetrical & dark brown in colour. Its length is 2 to 4 cm & width is 1 to 1.5 cm. There are two black spots on the dorsal side of the pronotum of the thorax.
Sexual dimorphism :
It exhibits distinct sexual dimorphism i.e. male and female can be distinguish on the basis of external features. These differences are as follows-
- Male cockroach
- Female cockroach
Segmentation :
The cockroach exhibits metameric segmentation. There are total 20 segments during embryonic stage but 19 segments during adult stage. The body is divisible into
head, thorax & abdomen.
(A) Head –
The head is attached to the thorax at 90° with the help of a thin & elastic neck. It is triangular & pear shaped. The head in cockroach is hypognathus. It is formed by the fusion of 6 segments. One pair of compound eyes are situated on the head which are black & kidney-shaped.
There is a pair of simple eyes or ocellar spots or fenestra or ocelli which are situated near the compound eyes. They are non-functional & less developed. There is no image formation in the ocelli but they’ are sensitive to light. (Photosensitive)
The cockroach has a pair of antennae which are movable situated on the head in the antennary sockets near the compound eyes. Each antenna has three parts-
- Scape—Basal part which articulates to the head.
- Pedicel—Middle part which is provided with Jonston organ. The Johston organs are sensory to antennary movements.
- Flagullum—It is a thread-like & multi-segmented structure which is provided withe thigmoreceptors & olfactoreceptors.
The antennae of the cockroach are thin, long, filliform & monolifonn.
(B) Thorax –
It forms 2/5 part of the body and It has three segments viz.—prothorax, mesothorax & metathorax. The thorax has 3 pairs of legs and 2 pairs of wings. It bears 2 pairs of spiracles or stigmata which are situated ventrolaterally on pro-mesothorax & meso- metathorax.
(C) Abdomen –
It bears 11 segments during embryonic stage but 10 segments in adults. The abdomen is without locomotory organs. First eight abdominal segments bears 8 pairs of spiracles. The first abdominal segment is smallest.
There is a pair of scent glands between the 5th & 6th abdominal segments. Their secretions keep the enemies away. According to some scientists these secretions act as sex attractant.
The abdomen bears a pair of anal cerci which are attached to the 10 th tergite in both male & female cockroaches. The anal cerci are long. thin. 15-segmented and provided withe phonoreceptors.
Male cockroach has a pair of small & pointed anal styles which are attached to the 9th sternite. They are unsegmented and help in copulation.
The anus is found at the end of the 10th segment in both male & female which is bounded by four chitinous plates viz.—epiproct-1, hypoproct-1 & paraproct-2. These podial plates are considered as the remnants of the 11th abdominal segment.
Female gonopore is found on the ventral side of the 8th abdominal segment and the male gonopore is found ventrally in the 9 the abdominal segment.
Both the male & female gonopores are provided with chitinous plates which are called as gonopophysis. The gonopophvsis are called as external genetelia or phallomeres. The female gonopophysis are called as ovipositors. The female gonopore remains covered by two gynovalvular plates which are modified 7th sternite.
Skeleton :
The cockroach bears both exoskeleton & endoskeleton.
(A) Exoskeleton
The body of cockroach is covered by chitinous exoskeleton which is dark brown in colour. The chitin is an acetate of glycosamine. The exoskeleton of each segment is called as sclerite which consists of four plates viz.—
- Tergum—one. dorsal & large
- Sternum—one. ventral & small
- Pleura—two, lateral & smallest
The sclerites remain connected by a thin & elastic membrane which is called as articular or arthrodial membrane. The chitin is soluble in water but it imparts hard nature to the exoskeleton
(a) Exoskeleton of head :
Exoskeleton of the head is called as head capsule which is formed by the fusion of six sclerites. The head capsule has 6 chitinous plates. The top of the head capsule is called as vertex which is divisible into two epicranial plates with the help of an epicranial suture. There is a frons plate just below the vertex & in front of the head capsule. The frons is followed by an oval plate, the clypeus. Both the lateral sides of the head capsule are made up of one-one gena plates which are also called as cheek plates. The head capsule bears an occipital foraman.
(b) Exoskeleton of neck :
The neck is covered withe 4 chitinous cervical plates. Out of them two arc dorso-lateral plates & two are ventro-lateral plates.
(c) Exoskeleton of thorax :
The sclerites of prothorax, mesothorax and metathorax are respectively called as pronotum, mesonotun & metanotum. The pronotum is the largest sclerite.
(d) Exoskeleton of abdomen :
The abdomen has 10 sclerites which are comparatively thin. In male the 7th tergite covers the 8th tergite. Similarly, the 7th stemite covers the 8the stemite. In female, 7th tergite covers 8th & 9th tergites and 7th stemite covers 8th & 9th stemites. In both male & female cockroaches 10th tergite is large & bilobed posteriorly.
(B) Endo skeleton
At many places, the exoskeleton in pushes to form endo skeleton to provides site for the attachment of muscles. The head bears a tent-like endo skeleton which is called as tentorium. The tentorium has a forman which allows nerves to pass through it.
The dorsal in pushing of the exoskeleton in the thorax are called apodedmes or phragma. There are three phragma viz.—
- First phragma— Betweem pronotum & mesonotum.
- Second phragma— Between mesonotum & metanotum.
- Third phragma— Between metanotum & first abdominal segment.
The ventral apodemes in the thorax are called as furca which are Y shaped.
