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, 
