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 Diaptoynus 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 regnnen by capturing larger 

 species of Entomostraca, especially Daphnia and Limnocalanus. 



A few words respecting the relative abundance of these species 

 at diiferent 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 tlie 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 tliis fact, I am indebted less to my own ob- 

 servations (which are, liowever, consistent with it as far as they go) than 

 to the statements of B. W. Tliomas, Esq., of Chicago, who, while making 

 a specialty of the Diatomacefe 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. 



