INTRODUCTION 



I. Distinction of Batrachians from Fishes and Reptiles 



The Batrachians represent a Class of Vertebrate animals 

 occupying a position between Fishes and Reptiles. There is con- 

 siderable variation in general appearance among the different 

 living members of the Class, so that a Batrachian is not as easily 

 defined and identified as is a fish, a bird, or a mammal.' There 

 is no one characteristic by which it may be known, as there is 

 in each of these other Classes. 



Batrachians, however, are distinguished from Fishes by sev- 

 eral easily recognizable characteristics. They usually have paired 

 limbs furnished with fingers and toes (pentadactyle limbs), and 

 never have fins stiffened by bony rays (although they may have 

 fins soft and filmy in character in the young stages). With the 

 exception of one order (Apoda), they do not have scales, but pos- 

 sess a skin either smooth and slimy or rough with warts and 

 nearly dry. Fishes breathe throughout their lives by means of 

 gills, but the Batrachians, while usually living in the water and 

 breathing by gills in the early stages of life, as a rule breathe 

 during adult life by means of lungs, and are more or less well 

 developed for land life.^ 



A popular distinction from the Reptiles is not easily made, 

 since Batrachians and Reptiles sometimes correspond almost ex- 

 actly in form. That is, they both have limbs of the pentadactyle 

 type and in the case of Salamanders (Batrachians) and Lizards 

 (Reptiles) both possess tails and elongated bodies. In fact, some 

 of the common Salamanders are popularly called Lizards, show- 

 ing the great superficial resemblance of certain members of the 

 two Classes. 



However, Batrachians and Reptiles are very different indeed 

 in all fundamental points. Instead of a more or less smooth and 

 slimy skin, Reptiles have a skin protected by overlapping scales, 



•There are certain technical points of difference in characteristics of the skeletons; i.e., the 

 vertebrae of Fishes are never pseudocentrous or notocentrous. The Batracliian has two occipital con- 

 dyles, except in the case of some Stegoccphali. The Batrachian is characterized by the presence of a 

 fenestra ovalis and stapes and by internal nares. 



I 



