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  • Structural Organisation in Plants and Animals
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Cockroach

- Cockroaches are brown or black bodied animals that are included in class Insecta of Phylum Arthropoda.

- Bright yellow, red and green coloured cockroaches have also been reported in tropical regions.

- Their size ranges from ¼ inches to 3 inches (0.6-7.6 cm) and have long antenna, legs and flat extension of the upper body wall that conceals head.

- They are nocturnal omnivores that live in damp places throughout the world. 

Morphology:

  • The adults of the common species of cockroach, Periplaneta americana are about 34-53 mm long with wings that extend beyond the tip of the abdomen in males.

  • The body of the cockroach is segmented and divisible into three distinct regions - head, thorax and abdomen

  • The entire body is covered by a hard chitinous exoskeleton (brown in colour).

  • In each segment, exoskeleton has hardened plates called sclerites (tergttes dorsally and sternites ventrally) that are joined to each other by a thin and flexible articular membrane (arthrodial membrane).

  • 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 arises 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.

  • 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 gerutal 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.

  • 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 forstoring of food. The crop is followed by gizzard or proventriculus. It has an outer layer of thick circular muscles and thick inner culicle 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 caecae 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 Malphigian 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. 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.

Q. 1 - Excretion in cockroach takes place by         

(a) Nephridium   

(b) Coxal glands   

(c) Parotid gland 

(d) Malpighian tubules

Q. 2 - Correct order of excretory organs in Cockroach, Earthworm and Rabbit respectively

(a) Skin, malpighi tubules, kidney                

(b) Malpighi tubules, nephridia, kidney

(c) Nephridia, malpighi tubule, kidney      

(d) Nephridia, kidney, green gland

Q.1

Q.2

d

b

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