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Spermatogenesis note graduation

SKULL TYPES IN REPTILES, IAS ZOOLOGY

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                                 SKULL TYPES IN REPTILES Reptiles are ectothermic animals whose body is covered by epidermal scales . They possess monocondylic skull that rests on a long neck made of atlas, axis and other cervical vertebrae . They have two sacral vertebrae, which are fused together to transfer the weight of body onto the hind limbs. Pentadactyle limbs bear sharp claws which help the animal in creeping and climbing. Reptiles were the first vertebrates that laid a large, shelled, cleoid egg that could develop on land. The egg has three membranes, amnion, allantois and yolk sac which help in the development of the embryo on land in dry conditions. Generally in reptiles with big jaws and large head, the skull becomes too heavy for the neck to support it. Therefore vacuities or fossae developed in reptiles to lighten the skull and also to provide space for accommodating powerful jaw muscles. The skull names come from the word “ apse ,” which means “ arch .” The numbe
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ORIGIN & EVOLUTION OF REPTILES , IAS ZOOLOGY UPSC

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  ORIGIN & EVOLUTION OF REPTILES Reptiles evolved from amphibians of Carboniferous period , which depended on water bodies for laying eggs and development of larval stages and hence could not exploit arid habitats far away from water bodies. They invented a large yolk-laden shelled egg that could be laid on land and in which an amniotic sac contained fluid in which embryo could develop to an advanced stage , capable of fending for itself when hatched. The following anatomical changes transformed the ancestral amphibians into land adapted reptiles: Body developed a covering of epidermal scales to prevent loss of body moisture, and skin glands were lost . Skull became monocondylic for better movement and flexibility. Atlas and axis vertebrae together permitted skull movement in all directions. Limb bones and girdles became stronger but limbs were attached on the sides of body , and belly touched the ground during creeping mode of locomotio
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Migration of Birds: Kinds and Modes | Vertebrates | Zoology ,UPSC

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  Migration of Birds: Kinds and Modes | Vertebrates | Zoology Contents: 1.     Migratory and Resident Birds 2.     Kinds of Migrations 3.     Modes of Flight in Migration 4.     Problems of Migration 5.     Advantages and Disadvantages of Avian Migration 1. Migratory and Resident Birds: Migration is a periodic passing of animals from one place to another (Cahn). Bird’s migration is a two-way journey , i.e., a regular, periodic, to-and-fro movement of some birds between their summer and winter homes or from a breeding and nesting place to a feeding and resting place. Majority of birds have the inherent quality to move from one place to another to obtain the advantages of the favourable condition . Such birds are called migratory birds. Some birds such as bobwhite and ruffled sand grouse, however, do not migrate at all and they remain throughout the year in a country. Such birds are called resident birds. Migratory birds cover thousands of miles in their period
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