[II] THE FIRST FOOD OF THE COMMON WHITEFISH. 781 



were eating increased rapidly the longer the fishes were kept in the 

 aquarium. Only one-fourth of those examined on the 14th of the month 

 had taken food, while more than five-sixths of those bottled ten days 

 later had already eaten. The entire number of objects appropriated 

 by these sixty-three fishes was as follows : Cyclops #/«om«si, ninety-seven; 

 Diaptomm sicilis, seventy-eight; Amircea striata, twenty-nine; Daph- 

 nia hyalina, one. Seven of the fishes had eaten unicellular Algae, two 

 had eaten diatoms, and one filamentous Algee. 



From the above data we are compelled to conclude that the earliest 

 food of the whitefish consists almost wholly of the smallest species of 

 Entomostraca occurring in the lake, since the other elements in their 

 alimentary canals were evidently either faken accidentally or else ap- 

 peared in such trivial quantity as to contribute nothing of importance 

 to their sujiport. In fact, two species of Copepoda, Cyclops thomasi and 

 Diatomtis sicilis, are certainly very much more important to the main- 

 tenance of the whitefish in this earliest stage of independent life tban 

 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 Lim- 

 nocalanus. 



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 excellent 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 intro- 

 duction 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 increase in numbers and rate of multiplica- 

 tion, in Lake Michigan there is but little difference in the products of 

 the collecting apparatus at different seasons of the year.* There is a 

 shght 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 dis- 

 tributed, 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 more densely populated by these animals than the 

 lake itself, as has been particularly evident at Eacine and South Chi- 



* For definite assurance of this fact, I am indebted less to my own observations 

 (whicli 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 Diatoniacea' 

 of the lake, has collected and studied all its organic forms for several years, obtain- 

 ing them from the city water by attaching a strainer to a hydrant many times during 

 every month throughout the year, 



