782 REPORT OF COMMISSIONER OE EI«1I AND FISHERIES. [12] 



cago. Neither are tbey 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 tish-culturist that the particular 

 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 Entomos- 

 traca 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 Commissoner, Prof. S. F. Baird, and to Frank K 

 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. 



