FROGS. 19 



reduced to a much lower number of species. There are now but 

 little more than 1,500 species of Reptiles and Batrachians described, 

 and only 100 of those belong to Europe.* 



I. Batrachia. 



Animals which compose this class have long been confounded 

 with reptiles, from which they differ in one fundamental pecu- 

 liarity in their organization. At their birth they respire by 

 means of gills, and consequently resemble fishes. In a physio- 

 logical point of view, at a certain time in their lives, these 

 animals are fishes in form as well as in their habits and orga- 

 nization. As age progresses, they undergo permanent meta- 

 morphosis — they acquire lungs, and thenceforth an aerial 

 respiration. It is, then, easy to understand that these animals 

 hold a doubtful rank, as they have long done, amongst Reptiles, 

 which are animals with an aerial respiration ; they ought to form a 

 separate class of Yertebrates.f 



Batrachians establish a transitional link between Fishes and 

 Reptiles — they are, as it were, a bond of union between those two 

 groups of animals. In the adult state Batrachians are cold-blooded 

 animals with incomplete circulation, inactive respiration, and the 

 skin is bare. In the introductory section to this chapter we have 

 given the general characteristics which belong to them. The 

 Frogs — Tree Frogs, Toads, Surinam Toads, Salamanders, and 

 I^ewts-^— are the representatives of the principal families of 

 Batrachians of which we propose giving the history. 



The Frogs, Rana, have been irreparably injured by their resem- 

 blance to the Toads. This circumstance has given rise to an unfa- 

 vourable prejudice against these innocent little Batrachians. Had 

 the Toad not existed, the Frog would appear to us as an animal 

 of a curious form, and would interest us by the phenomena of 

 transformation which it undergoes in the different epochs of its 

 development. We should see in it a useful inoffensive animal of 

 slender form, with delicate and supple limbs, arrayed in that 



* Vide subsequent notes on this subject, in p. 31, &o. 



t Tbey are regarded by some naturalists as a sub-class of Fishes rather than of 

 Reptiles, as piscine forms certain of which develop to a parallelism with the ordinary 

 reptilian condition of advancement ; their reproduction especially favouring this 

 view or idea. — Ed. 



c2 



