VOYAGE FEOM NEW YORK TO RIO DE JANEIRO. 25 
of these immense Mammalia. I believe that the embryonic 
changes of the sloths and armadillos will explain the struc- 
tural relations of those huge Edentata and their connection 
with the present ones. South America teems with the fossil 
bones of these animals, which indeed penetrated into the 
northern half of the hemisphere as high up as Georgia and 
Kentucky, where their remains have been found. The 
living representatives of the family are also numerous in 
South America, and we should make it one of our chief 
objects to get specimens of all ages and examine them from 
their earliest phases upward. We must, above all, try not to 
be led away from the more important aims of our study by 
the diversity of objects. I have known many young natu- 
ralists to miss the highest success by trying to cover too 
much ground, by becoming collectors rather than investi- 
gators. Bitten by the mania for amassing a great number 
and variety of species, such a man never returns to the 
general consideration of more comprehensive features. We 
must try to set before ourselves certain important questions, 
and give ourselves resolutely to the investigation of these 
points, even though we should sacrifice less important 
things more readily reached. 
" Another type full of interest, from an embryological 
point of view, will be the Monkeys. Since some of our scien- 
tific colleagues look upon them as our ancestors, it is impor- 
tant that we should collect as many facts as possible concern- 
ing their growth. Of course it would be better if we could 
make the investigation in the land of the Orangs, Gorillas, 
and Chimpanzees, the highest monkeys and the nearest to 
man in their development. Still even the process of growth 
in the South American monkey will be very instructive. 
Give a mathematician the initial elements of a series, and 
