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Study of animal types: Cockroach

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  • BioAdmin
    started a topic Study of animal types: Cockroach

    Study of animal types: Cockroach

    • Cockroaches are brown or black bodied animals that are included in class Insecta of Phylum Arthropoda.
    • They have long antenna, legs and flat extension of the upper body wall that conceals head.
    • They are pests because they destroy food and contaminate it with their smelly excreta and also transmit various types of bacterial diseases.

    Morphology
    • The adults of the common species of cockroach, Periplaneta americana are about 34-53 mm long with wings 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.
    • In each segment, exoskeleton has hardened plates called sclerites joined to each other by arthrodial membrane.
    • Head is triangular in shape formed by the fusion of six segments, which bears a pair of compound eyes.
    • Antennae arise from membranous sockets lying in front of eyes and anterior end of the head bears appendages.
    • The mouthparts consisting of a labrum, a pair of mandibles, a pair of maxillae and a labium and a median flexible lobe, acting as tongue.
    • Thorax consists of three parts – prothorax, mesothorax and metathorax and the head is connected with thorax by a short extension of the prothorax known as the neck.
    • The first pair of wings arises from mesothorax and the second pair from metathorax.
    • Forewings called tegmina are opaque dark and leathery and cover the hind wings.
    • The abdomen in both males and females consists of 10 segments.
    • In females, the 7th sternum 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, which contains dorsal anus, ventral male genital pore and gonapophysis.
    • 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, opens into a sac like structure called crop.
    • Crop has an outer layer of thick circular muscles and thick inner culicle forming six highly chitinous plate called teeth.
    • 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.
    • Hindgut is differentiated into ileum, colon and rectum and the rectum opens out through anus.
    Digestive system of cockroach
    • Blood vascular system of cockroach is an open type and blood vessels open into haemolymph.
    • The haemolymph is composed of colourless plasma and haemocytes.
    blood vascular system of cockroach
    • The respiratory system consists of a network of trachea, that open through 10 pairs of small holes called
    • The opening of the spiracles is regulated by the sphincters and exchange of gases take place at the tracheoles by diffusion.
    • Excretion is performed by Malpighian tubules, which are lined by glandular and ciliated cells and absorb nitrogenous waste products and convert them into uric acid, hence the organism is uricotelic.
    • The nervous system of cockroach consists of a series of fused, segmentally arranged ganglia.
    • The brain is represented by supra-oesophageal ganglion which supplies nerves to antennae and compound eyes.
    • The sense organs are antennae, eyes, maxillary palps, labial palps, anal cerci, etc.
    • Each eye consists of about 2000 hexagonal ommatidia, due to a cockroach can receive several images of an object, which is known as mosaic vision or nocturnal vision.
    • Male reproductive system consists of a pair of testes lying one on each lateral side in the 4th-6th abdominal segments.
    • From each testis arises a thin vas deferens, which opens into ejaculatory duct through seminal vesicle and the ejaculatory duct opens into male gonopore situated ventral to anus.
    • In the 6th-7th abdominal segments there is an accessory reproductive gland.
    • The sperms are stored in the seminal vesicles and are glued together to form spermatophores.
    • The female reproductive system consists of two large ovaries in the 2nd – 6th abdominal segments.
    • Each ovary is formed of a group of eight ovarian tubules or ovarioles, containing a chain of developing ova.
    • Oviducts of each ovary unite into a single median oviduct.
    • Sperms are transferred through spermatophores.
    • Their fertilized eggs are encased in dark reddish to blackish brown capsule called oothecae.
    • The development of P. americana is paurometabolous, in which development takes place through nymphal stage.

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