VOYAGE FROM 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 thorn 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 



