Useful information on morphology of cockroach

The cockroach has a long dorsoventrally flattened segmented body and rich-brown red in colour. It is about 35-38 mm long and 10-12 mm broad. The body is externally covered by a hard chitinous exoskeletons secreted by underlying cells. The exoskeletons provides surface for attachment of muscles and also protect the body. The body is divided into 3 parts i.e. head, thorax, and abdomen.

Head:

The head is pear shaped or triangular. The exoskeleton of the head is known as epicranium. It consists of six chitinous plates or sclerities. The top of the head is covered by a pair of epicranial plates joined in front by a Y-shaped epicranial surface. Below the epicranial plate, there lies a single large triangular plate called frons. Below the frons is a small rectangular plate called clypeus. Hinged on the clypeus is a movable plate called labrum. The labrum forms the upper lip. On either side of the head lies a vertical plate called gena. On the upper part of the head on their side, there are two large compound eyes. Inner to each eye lies a shallow depression on the frons called atennal socket. Inner to each antennal socket is a white rounded patch called fenestra. It represents the reduced simple eye or ocellus found in other insects.

A pair of long multi-joined, thread –like movable structure the antenna is attached in front of eyes. Each antenna articulates in membranous pit or antennal socket and has 3 partnership these-basal scape, middle pedical and terminal long many jointed flagellum. These are organs of touch and smell.

Mouth Parts:

The appendages found around the mouth are called mouth parts. They are chewing and mandibulate type. Mouth part consists of a labrum, a pair of mandible, a pair of first maxillae, a labium and a hypopharynx.

(i) Labrum:

It is a broad flat lobe suspended below the clypeus. It acts as the upper lip. It is moved by the muscles present on its base.

(ii) Mandibles:

A pair of mandibles lies below the genae. Each mandible is a stout, unjointed structure having teeth on its inner edge. The mandibles move from side to side to cut and masticate the food with adductor and adductor muscels.

1st Maxillae:

A pir of maxillae lies below the mandible. Each maxilla is a biramous appendage consists of 3 parts- the basal protoprodite, inner endopodite and outer exopodite. The protopodite is made of two joints- proximal cardo and distal stipes.Exopodite is a five jointed structure, the maxillary palp, which arises from a small palpifer (a small projection). Endopodite is internal to maxillary palp and is made upon of twp pieces, outer galea and inner lacinia. The maxillae serve to hold the food by the claws of their lacinia and bring it to the mandible for mastication. They are also used for cleaning the antenna and 4 legs.

Labium or second maxilla or lower lip: Labium lies behind first pair of maxillae. It is formed by fusion of cardo and stipes of second pair of maxillae. It consists of three parts- the upper broad sub-mentum the middle small mentum and the lower pre-mentum. The endopodites form an inner glossa and an outer paraglossa. The pre-mentum bears on each side a three jointed labial palp. The labial palp is present on a small projection known as palpiger. The palp bears bristles that act as sense organs. The glossae and paraglossae help in pushing the masticated food into the pre-oral cavity.

Hypopharynx or Lingua:

It is a median tounge like structure hanging in the pre-oral cavity between 1^st maxillae. It bears the opening of the salivary gland.

Neck:

The neck is a short slender flexible tube movable articulating the head with thorax. It is supported by a few rings like sclerites. It is only an extension of articular membrane.

Thorax:

The thorax consists of 3 segemnts- anterior prothorax, middle mesothorax and posterior metathorax. Each thoracic segment is covered dorsally by a sclerite, the tergum or notum ventrally by another scherite, the sternum and laterally by two cuticular pleura.Terga, sterna and pleura are joined with one another arthrodial membrane.

Each thoracic membrane bears a pair of walking legs. Thus there are 3 pairs of legs called prothracic, mesothoracic and metathoracic legs. Each segement consists of five parts: coxa, Trochanter, Femur, tibia and Tursus is the lower most part of leg consisting of five segments called tarsomeres. Each tarsomere bears an adhesive pad called plantuala. The lat tursal segment is often called pre-tursus. It ends into two curved claws which a soft adhesive pad called arolium or pulvillus.

Wings:

The mesothorax and metathorax have each a pair of wings attached to terga dorsally. Each wing is an expansion of cuticle supported by a network of chitinous ridges called nervures or veins. The anter pair of fore wings are narrows, brownish and opaque and it is very leathery in texture. They form a protecting covering for the hind wigs at rest. Therefore they are known as wing covers or tegmina. The hind wings are thin, membranous, transparent and used in flight.

Abdomen:

The abdomen consists of ten segments in adult, eleven in embryo. Typically each segment has its own dorsal tergum and ventral sternum. The 8^th and 9 that terga of female and only 9^th tergum of male are covered by 7^th tergum. The 10^th tergum projects backwards beyond the abdomen as a bilobed sclerite and there are only nine sterna plates. In the female the 8^th and 9^th sterna are invaginated and completed concealed by the enlarged boat shaped 7^th sternum. The 7^th sternum encloses a big space called oothecal chamber or gynovalvular chamber, when oothecas are formed.

In males the 8^th and 9^th sterna are concealed by 7^th sternum which projects a pair of unjointed anal styles. Anal styles are absent in female is produced backward into a pair of large oval opical lobes or gynovalvular plates which from a keel like structure, which distinguishes the female from the male. The genital structures in both sexes are surrounded by sclerites called gonoapophyses .In male they form external genitalia. In female the gonopophyses form an ovaipositor. In the 10^th segment just below the tergum, is the anus is supported by four podicel plates. In both sexes the tenth tergum bears a pair of long tapering jointed analcerci.

Spiracles or Stigmata:

There are 10 pairs of slit like apertures called spiracles lead in to lateral side of the body. The spiracles lead into respiratory air tubes called trachea.

Stink Gland:

The intersegmental membrane between the 5^th and 6^th terga is depressed on either side of the stink gland. These glands produce a secretion with a characteristic odour.