66 



in Lake Michigan there is but httle 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 more densely populated by 

 these animals than the lake itself, as has been particularly 

 evident at Racine and South Chicago. Neither are they 

 commonly equally distributed throughout the waters in which 

 they are most abundant, but like most other aquatic animals, 

 occur in shoals. In the deeper portions of the lake, many 

 species shift their level according to the time of day, coming 

 to the surface by night and sinking again when the sun is 

 bright. 



These facts make it important to the fish-culturist that the 

 particular situation when it is proposed to plant the fry should 

 be searched at the time when these are to be liberated, to 

 determine whether they will find at once sufficient food for their 

 support. A little experience will easily enable one to estimate 

 the relative abundance of the Entomostraca at any given time 

 and place, and they require nothing for their capture more com- 

 plicated or difficult of management than a simple net of cheese- 

 cloth or similar material, towed behind a boat. This may be 

 weighted and sunk to any desired depth, so that the contents 

 of the water either at the surface or at the bottom, may be 

 ascertained by a few minutes' rowing. 



State Laboratory of Natural History, Champaign, III. 



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

 however, consistent with it so 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. 



