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| Summary |
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 Animals can be broadly distinguished into two major groups: |
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 The Nonchordates (or invertebrates) |
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 The chordates |
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 Nonchordates are animals which do not have a vertebral column or a |
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| backbone. Earthworm and cockroach are examples of nonchordates. |
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 Chordates are animals which have a notochord on the dorsal |
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| side of the body. Frog and rat are examples of chordates. |
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 Pheretima posthuma is a common species of earthworm found living in burrows made in moist soil. It is nocturnal in habit. |
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 It has an elongated, cylindrical body which is metamerically segmented. |
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 Bodywall consists of a thin cuticle, epidermis and musculature. |
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 Body cavity is a true coelom since it is lined by a layer of coelomic epithelium of mesodermal origin. |
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 The coelomic fluid present inside the coelom contains four types of cells namely, Phagocytes, Mucocytes, Round Nucleated cells |
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| and Chloragogen cells. |
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 Locomotion involves musculature of the bodywall and structures called setae. |
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 Earthworms feed on dead organic matter, particularly vegetation present in the soil. |
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 Circulatory system is of closed type, consisting of blood vessels and capillaries which ramify to all parts of the body. The blood is composed of plasma and corpuscles. |
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 Excretion is carried out by segmentally arranged coiled ducts called nephridia. |
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 Nephridia can be distinguished into three types: |
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| Pharyngeal, Integumentary, Septal nephridia. |
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 Respiration occurs through the bodywall by simple diffusion. |
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 Nervous system is well developed. |
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 Reproduction is only by sexual method. |
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 Development is direct. |
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 Periplaneta americana is one of the several species of cockroaches that inhabit our country. |
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 Cockroach is a nocturnal, omnivorous animal. It feeds on any kind of organic matter. |
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 Cockroach has a dorso ventrally flat, compressed body which is covered by a hard, chitinous exoskeleton. |
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 The head is a region formed by the fusion of six embryonic segments covered by very hard exoskeletal plates called sclerites. |
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 The head is triangular in shape. |
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 The head bears a pair of compound eyes, a pair of antennae, a mouth |
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| and a group of appendages collectively known as mouthparts (trophi). |
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 The thorax is formed by three independent segments: |
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| prothorax, mesothorax and metathorax. |
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 The abdomen consists of 10 segments. |
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 The body of the frog can be distinguished into head and trunk. |
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 The head is triangular in shape and it contains a mouth, a pair of nostrils and retractible eyes. |
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 The trunk merges with the head and lacks a neck. The trunk bears a pair of forelimbs and a pair of hind limbs. |
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 The general body cavity which is called coelom gets partitioned into numerous cavities. |
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| They are the cranial cavity, orbital cavities, nasal cavities, buccal cavity, spinal cavity, thoracic cavity and abdominal cavity. |
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 The skeleton can be distinguished into an axial skeleton and an appendicular skeleton. |
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 Alimentary canal is distinguished into an oesophagus, a stomach, a small intestine and a large intestine. |
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 Circulatory system consists of heart, blood vessels and blood. |
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 Respiratory system consists of a pair of lungs, a pair of bronchi and a trachea. |
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 Excretory system is represented by a pair of kidneys, a pair of ureters and a urinary bladder. |
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 Nervous system is represented by a brain, a spinal cord, cranial nerves, |
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| spinal nerves and the autonomic (sympathetic and parasympathetic) nerves. |
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 Development is indirect. Significant changes take place during the transformation of the tadpole into a young adult. This is called metamorphosis. |
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 Rat is a nocturnal, household pest. |
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 The rat has an elongated body which can be distinguished into a head, a trunk and a tail. |
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 A relatively shorter neck connects the head to the trunk. |
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 The tail is long and has a covering of small overlapping scales. It is primarily used as a balancing organ. |
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 The skeleton of rat has 223 bones that are distributed into the axial skeleton and the appendicular skeleton. |
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 The rat has a well developed Digestive System. |
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 The circulatory system is well developed. |
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 Lungs are the respiratory organs. |
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 The Excretory system is represented by the kidneys, the ureters and the urinary bladder. |
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 The nervous system consists of a central nervous system, a peripheral nervous system and an autonomic nervous system. |
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