108 
The First Food of the Common White-Fish. 
From the above data we are compelled to conclude that the 
earliest food of the white-fish consists almost wholly of the small- 
est species of Entomostraca occurring in the lake, since the other 
elements in their alimentary canals were evidently either taken 
accidentally, or else appeared in such trivial quantity as to contrib- 
ute nothing of importance to their support. In fact, two species 
of Copepoda, Cyclops thomasi and Diaptomus sicilis , are certainly 
very much more important to the maintenance of the white-fish in 
this earliest stage of independent life than all the other organisms 
in the lake combined. As the fishes increase in size, vigor, and 
activity, they doubtless enlarge their regimen by capturing larger 
species of Entomostraca, especially Daphnia and Limnocalanus. 
A few words respecting the relative abundance of these species 
at different seasons of the year and their distribution in the lake, 
will have some practical value. We may observe here an excel- 
lent illustration of the remarkable uniformity of the life of the 
lake as contrasted with that of smaller bodies of water already 
referred to, in the introduction to this paper. While in ponds 
minute animal life is largely destroyed or suspended during the 
winter, the opening spring being attended by an enormous in- 
crease in numbers and rate of multiplication, in Lake Michigan 
there is but little difference in the products of the collecting 
apparatus at different seasons of the year.* There is a slight 
increase in the number of individuals during spring and early 
summer, but scarcely enough appreciably to affect the food 
supply of fishes dependent upon them. They are not by any 
means equally distributed, however, throughout the lake, my own 
observations tending to show that there are relatively very few of 
these minute crustaceans to be found at a distance of a few miles 
from shore, and that in fact by far the greater part of them usually 
occur within a distance of two or three miles out. Indeed, the 
mouths of the rivers flowing into the lake are ordinarily much 
*For definite assurance of this fact, I am indebted less to my own ob- 
servations (which are, however, consistent with it as far as they go) than 
to the statements of B. W. Thomas, Esq., of Chicago, who, while making 
a specialty of the Diatomacese of the lake, has collected and studied all 
its organic forms for several years, obtaining them from the city water by 
attaching a strainer to a hydrant many times during every month 
throughout the year. 
