EMBRYOLOGY AND CLASSIFICATION. 299 



full of promise. Embryologists have generally 

 considered their work as complete when they 

 have traced the new being to a point at which 

 it resembles somewhat any of the members of 

 the natural group to which it belongs. The 

 process by which the gradual completion of the 

 whole frame is attained has been assumed to 

 be one of little interest, hardly deserving the 

 careful scrutiny of the embryologist ; while the 

 zoologist has also overlooked, or regarded as of 

 little importance, the differences which still dis- 

 tinguish the young from the adult, even after 

 its typical characters are perfectly distinct. Yet 

 naturalists might have taken a hint from one 

 class of Vertebrates long known for their pecu- 

 liar metamorphoses, and which show how im- 

 portant are the facts to be learned from these 

 early stages in the life of any animal. 



More than a century ago Roesel, in his masterly 

 work on the Frogs and Toads of Germany, repre- 

 sented the mode of reproduction and growth 

 of these animals with a remarkable degree of 

 accuracy, and this subject has since been traced 

 with additional precision and minuteness by Rus- 

 coni, Yon Siebold, and Funke. Notwithstanding 

 this, no special application has yet been made 

 of the results of these investigations to the clas- 

 sification of these animals, beyond the general 

 recognition that the caudate Batrachians, with 



