Chapter 7 Structural Organization In Animals
Animal tissues are divided into four types:
In earthworm, the body is covered by cuticle. All segments of its body are alike except the 14th, 15th and 16th segment. A ring of S-shaped chitinous satae is found around each segment. These help in locomotion. On the ventral side, spermathecal openings are present. The alimentary canal is a narrow tube made of mouth, buccal cavity, pharynx, gizzard, stomach, intestine and anus. The blood vascular system is of closed type with heart and valves. Nervous system is represented by ventral nerve cord. Earthworm is a hermaphrodite.
The body of a cockroach is covered by chitinous exoskeleton. It is divided into head, thorax and abdomen. Segments bear jointed appendages. There are three segments of thorax. Two pairs of wings are present. There are ten segments in the abdomen. Alimentary canal is well developed with a mouth surrounded by mouth parts, a pharynx, oesophagus, crop, gizzard, midgut, hindgut and anus. The blood vascular system is of open type. Respiration takes place by network of thrachae.
The body of the frog is covered by skin. Mucous glands are present in the skin which helps in respiration in water and on land. Body is divisible into head and trunk. A muscular tongue is present, which is bilobed at the tip and is used in capturing the prey. The alimentary canal consists of oesophagus, stomach, intestine and the rectum. The main digestive glands are the liver and pancreas. Circulatory system is closed with single circulation. Nervous system is organized into central, peripheral and autonomic.
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