PRELIMINARY CONSIDERATIONS. 



In order to make clear the positions which the two groups 

 under consideration hold in the animal scale, the following brief 

 scheme of classification is given : 



Szib-Phylum VERTEBRATA. — Animals with cartilaginous or 



osseous spinal column. 

 Class Cyceostomata. — The Hag-fishes and Lampreys. 

 Class Pisces. — The Fishes. 



Class Batrachia. — Skin 1 naked, not provided with scales. 

 Class Repttlia. — Skin covered with scales. 

 Class Ayes. — -The Birds. 

 Class Mammalia. — Those that suckle their young, as e.g., the 



horse, dog, man. 



From the above it will be seen that the living Batrachians 

 differ from the Reptiles by the former having a smooth skin, with- 

 out scales, while the reptiles have scales covering the body. The 

 early stages of Batrachia are spent in the water. The eggs are 

 laid there and develop into tailed larvae, commonly called " tad- 

 poles," which swim about for a certain period, breathing by 

 means of gills. Later, in the majority of species, the larvae 

 emerge from the water and assume a terrestrial mode of life, 

 breathing by means of lungs. The lower forms, however, such 

 as the salamander, require moisture, their lungs being poorly 

 developed, and one or two groups never leave the water, but 

 remain in their lowly condition, breathing by means of gills 

 throughout their lifetime. The higher forms, such as the toads 

 and frogs, on leaving the water, lose their tails and develop long 

 and strong hind legs for leaping. 



Passing to the Reptiles we have such diverse kinds of organ- 

 isms as the lizards, with four legs ; the snakes, which have 

 lost their legs, and the turtles, which have acquired a hard cover- 

 ing, the shell, to protect their bodies. 



Very frequently salamanders are taken by the uninitiated to 

 belong to the lizard group. From the considerations given above, 

 it is evident what the differences are and no confusion should be 



i. In the fossil Batrachia, to be spoken of later, the skin is covered with heavy bony 

 plates. 



