There is a slight increase in the number of individuals during the 

 spring and early summer, but scarcely enough appreciably to affect 

 the food supply of fishes dependent upon tliem. They are not by 

 any means eijually distributed, liowever, 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, bat 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 br:ght. 



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

 ticular situation where 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 complicated or difficult 

 of management than a simple ring 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. 



In conclusion, I wish again to express my great obligation to 

 the United States Fish Commissioner, Prof. S. F. Baird, and to 

 Frank N. Clark, Superintendent of the United States Hatchery at 

 Northville, Mich., through whom, as already stated, the specimens 

 were derived upon which these studies were made. My best thanks 

 are also due to the Exposition company of Chicago, and especially 

 to their Secretary, the Hon. John P. Reynolds, for the use of a 

 tank in the Exposition building, and for many courtesies received 

 while the experiment there was in progress. 



F. C.-ll 



