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, Von 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 
