Question

Draw a neat labelled external features of a cockroach.

Answer 1

Hint: Cockroaches are generalized insects, with few particular adaptations, and may be among the most primitive living Neopterin insects. They have a relatively small head and a broad, flattened body, and most species are reddish-brown to dark brown. They have large compound eyes, two ocelli, and long, flexible antennae.

Complete answer:
a. The cockroach has an elongated and segmented body. It is dark brown or reddish-brown. The exoskeleton of a cockroach is thick and is hardly made up of calcareous plates known as sclerites. There are a total of 10 segments. The segments on the dorsal side (or notum) are known as Tergum and segments on the ventral side are known as Sternum.
b. The exoskeleton in cockroaches is coated with wax, and hence it is impervious to water. It protects the loss of water from the body. It also provides rigidity and surface for attachment of body muscles. The arthrodial membrane joins the adjacent segments.
c. The body of a cockroach is divisible into three parts: head, thorax and abdomen. It has three pairs of jointed appendages and two pairs of wings. The fore wings are mesothoracic and are known as wing covers or tegmina or elytra. They cover and protect the hindwings. Forewings are dark, stiff, opaque and leathery. The hindwings of a cockroach are large, thin, membranous and transparent. These remain folded below the tegmina and are used for flying.
d. An opening called mouth is present on the ventral side of the head. It remains surrounded by five mouth parts, namely, a pair of mandibles, first maxillae, labium or fused second maxillae, hypopharynx and labrum. The mouthparts assist in biting and chewing its food.
e. Three pairs of legs are attached to a cockroach's thorax. The three pairs of legs are named according to the region of the thorax where it is present: prothoracic, mesothoracic and metathoracic legs.

Additional information: The alimentary canal of a cockroach is long and coiled. It is divided into three parts: foregut, midgut and hindgut. The foregut or stomodeum is further differentiated into five parts, namely, buccal chamber, pharynx, oesophagus, crop and gizzard. Midgut or mesenteron or ventriculus is short and tubular and is lined with glandular endoderm. Lastly, the hindgut is also known as proctodaeum. It comprises ileum, colon and rectum.

Note: The respiratory system of the cockroach consists of a network of the trachea which opens through ten pairs of small holes known as spiracles which are present on the lateral side of the body. Thin branching tubes, tracheal tubes subdivided into tracheoles, carry the oxygen from the air to all the parts of the body.