Explore the Morphology and Anatomy of Cockroach
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Answer:
Morphology
Head is triangular in shape and lies anteriorly at right angles to the
longitudinal body axis. It is formed by the fusion of six segments and
shows great mobility in all directions due to flexible neck .
The head capsule bears a pair of compound eyes. A pair of thread like
antennae arise from membranous sockets lying in front of eyes. Antennae
have sensory receptors that help in monitoring the environment. Anterior
end of the head bears appendages forming biting and chewing type of
mouth parts. The mouthparts consisting of a labrum (upper lip), a pair
of mandibles, a pair of maxillae and a labium (lower lip). A median flexible
lobe, acting as tongue (hypopharynx), lies within the cavity enclosed by
the mouthparts (Figure 7.15b). Thorax consists of three parts – prothorax,
mesothorax and metathorax. The head is connected with thorax by a
short extension of the prothorax known as the neck. Each thoracic segment
bears a pair of walking legs. The first pair of wings arises from mesothorax
and the second pair from metathorax. Forewings (mesothoracic) called
tegmina are opaque dark and leathery and cover the hind wings when at
rest. The hind wings are transparent, membranous and are used in flight.
The abdomen in both males and females consists of 10 segments. In
females, the 7th sternum is boat shaped and together with the 8th and 9th
sterna forms a brood or genital pouch whose anterior part contains female
gonopore, spermathecal pores and collateral glands. In males, genital pouch
or chamber lies at the hind end of abdomen bounded dorsally by 9th and
10th terga and ventrally by the 9th sternum. It contains dorsal anus, ventral
male genital pore and gonapophysis. Males bear a pair of short, threadlike anal styles which are absent in females. In both sexes, the 10th segment
bears a pair of jointed filamentous structures called anal cerci.
Anatomy
The alimentary canal present in the body cavity
is divided into three regions: foregut, midgut
and hindgut (Figure 7.16). The mouth opens
into a short tubular pharynx, leading to a
narrow tubular passage called oesophagus.
This in turn opens into a sac like structure
called crop used for storing of food. The crop
is followed by gizzard or proventriculus. It has
an outer layer of thick circular muscles and
thick inner cuticle forming six highly chitinous
plate called teeth. Gizzard helps in grinding the
food particles. The entire foregut is lined by
cuticle. A ring of 6-8 blind tubules called
hepatic or gastric caeca is present at the
junction of foregut and midgut, which secrete
digestive juice. At the junction of midgut and
hindgut is present another ring of 100-150
yellow coloured thin filamentous Malpighian
tubules. They help in removal of excretory
products from haemolymph. The hindgut is
broader than midgut and is differentiated into
ileum, colon and rectum. The rectum opens
out through anus.
Blood vascular system of cockroach is an
open type (Figure 7.17). Blood vessels are
poorly developed and open into space
(haemocoel). Visceral organs located in the
haemocoel are bathed in blood (haemolymph).
The haemolymph is composed of colourless
plasma and haemocytes. Heart of cockroach
consists of elongated muscular tube lying
along mid dorsal line of thorax and abdomen.
It is differentiated into funnel shaped chambers
with ostia on either side. Blood from sinuses
enter heart through ostia and is pumped
anteriorly to sinuses again.
The respiratory system consists of a
network of trachea, that open through 10 pairs
of small holes called spiracles present on the
lateral side of the body. Thin branching tubes
(tracheal tubes subdivided into tracheoles)
carry oxygen from the air to all the parts. The opening of the spiracles is regulated by the sphincters. Exchange of gases
take place at the tracheoles by diffusion.
Excretion is performed by Malpighian tubules. Each tubule is lined
by glandular and ciliated cells. They absorb nitrogenous waste products
and convert them into uric acid which is excreted out through the hindgut.
Therefore, this insect is called uricotelic. In addition, the fat body,
nephrocytes and urecose glands also help in excretion.
The nervous system of cockroach consists of a series of fused,
segmentally arranged ganglia joined by paired longitudinal connectives
on the ventral side. Three ganglia lie in the thorax, and six in the abdomen.
The nervous system of cockroach is spread throughout the body. The
head holds a bit of a nervous system while the rest is situated along the
ventral (belly-side) part of its body. So, now you understand that if the
head of a cockroach is cut off, it will still live for as long as one week. In
the head region, the brain is represented by supra-oesophageal ganglion
which supplies nerves to antennae and compound eyes. In cockroach,
the sense organs are antennae, eyes, maxillary palps, labial palps, anal
cerci, etc. The compound eyes are situated at the dorsal surface of the
head.
