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ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



AMPHIBIA 



SCHEME OF CLASSIFICATION 



I. Urodela (Tailed Amphibians). 



Cryptobranchus , Ampkiuma, Amblystoma, Salamandra, Triton, 

 Necturus, Proteus, Siren. 

 II. Apoda (or Gymnophiona — Burrowing, legless Amphibians). 



Coecilia, Hypogeophis, Epicrium. 

 III. Anura (Tailless Amphibians — Frogs and Toads). 

 Rana, Bufo, Hyla. 



The Amphibia form the first subdivision of the Tetrapoda. What 

 may be regarded as the normal form of body is that exemplified by a 

 Newt (Triton — Fig. 177, A). From this the Apoda and the Anura have 

 departed in different directions. The former (Fig. 180, B) have taken 



to a burrowing mode of life like that 

 of an Earthworm, and in correlation 

 with this the body has become very 

 long and cylindrical, bluntly pointed 

 at each end, and the limbs have 

 completely disappeared except for 

 minute and transient vestiges in 

 the embryo. In the Anura — Frogs 

 and Toads (Fig. 180, A)— on the 

 other hand the body has become 

 specialized for leaping : the hind- 



Aberrant types of body-form in the Amphibia. A, leaping type (Frog — Rana) ; B, burrowing 

 type (one of the Apoda — Hypogeophis). 



limbs have become greatly developed, their attachment has become 

 shifted far forwards so as to shorten the trunk region, while the tail, 

 large and protocercal in the larva or tadpole, atrophies and disappears 

 completely as the adult form is reached. 



The skin has, except for inconspicuous vestiges in a few members 

 of the group, lost all trace of the scales present in the fishes. Its 

 surface is soft and smooth, and is kept moist by the secretion of 



