VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 13 



" Our next aim, and with the same object, namely, its 

 bearing upon the question of origin, will be the study of the 

 young, the collecting of eggs and embryos. This is the 

 more important, since museums generally show only adult 

 specimens. As far as I know, the Zoological Museum at 

 Cambridge is the only one containing large collections of 

 embryological specimens from all the classes of the ani- 

 mal kingdom. One significant fact, however, is already 

 known. In their earliest stages of growth all animals of 

 the same class are much more alike than in their adult 

 condition, and sometimes so nearly alike as hardly to be 

 distinguished. Indeed, there is an early period when the 

 resemblances greatly outweigh the differences. How far 

 the representatives of different classes resemble one another 

 remains to be ascertained with precision. There are two 

 possible interpretations of these facts. One is that animals 

 so nearly identical in the beginning must have been origi- 

 nally derived from one germ, and are but modifications or 

 transmutations, under various physical conditions, of. this 

 primitive unit. The other interpretation, founded on the 

 same facts, is, that since, notwithstanding this material iden- 

 tity in the beginning, no germ ever grows to be different 

 from its parent, or diverges from the pattern imposed upon 

 it at its birth, therefore some other cause besides a material 

 one must control its development ; and if this be so, we have 

 to seek an explanation of the differences between animals 

 outside of physical influences. Thus far both these views 

 rest chiefly upon personal convictions and opinions. The 

 true solution of the problem must be sought in the study 

 of the development of the animals themselves, and embry- 

 ology is still in its infancy ; for, though a very complete 

 study of the embryology of a few animals has been made, 



