77S REPOKT OF COMMrSSlONEB OF FISH AND FISHEEIES. [8] 



note that I saw oue of the smallest fishes make a spring at a Cyclops, 

 catch it, jiive three or four violent wriggles, and drop it dead to the bot- 

 tom of the tank. 



As a general statement of the result of the observations made on 

 these fourteen fishes, we may say that eight of them ate a single Cyclops 

 each, that one took two, and another Miree of the same, that one took 

 a single Canthocamptns, that two specimens captured two each of this 

 genus, and that finally a single fish ate Cyclops and Canthocamptns 

 both. The final conclusion was a highly probable inference that the 

 smallest Entomostraca occuriug in the lake would prove to be the nat- 

 ural first food of the species. 



In order to test this conclusion with precision, 1 arranged a similar ex- 

 periment on a larger scale and under more natural conditions Through 

 the generosity of the Exposition Company, of Chicago, I was allowed 

 the use of one of the large aquarium tanks in the exposition building on 

 the lake shore, and by the repeated kindness of Mr. Clarke, of North - 

 yille, Mich., I was furnished with a much larger number of living white- 

 fish. Five thousand fry were shipped to me in a can of water, but through 

 unfortunate delays in changing cars at intermediate points, about two- 

 thirds of these were dead when they reached my hands. Those living 

 were immediately transferred to the tank" through which the water, 

 taken from the city pipes, had already been allowed to run for several 

 hours. As this water is derived from Lake Michigan at a distance of 

 two miles from the shore, and had at this time the exact temi)erature 

 of the open lake, the conditions for experiment were as favorable as 

 artificial arrangements could well be made. 



Sending a man with a towing net out upon the lake with a boat, or 

 ui)on the remotest breakwaters, immense numbers of all organic objects 

 in the water were easily obtained. After inclosing the exit of the tank 

 with a fine wire screen, to prevent the escape of objects placed in it, 

 we poured these collections of all descriptions indiscriminately into the 

 water from day to day, thus keeping the fishes profusely supplied with 

 all the various kinds of food which could possibly be accessible to them 

 in their native haunts. From this tank one hundred fishes were taken 

 daily and placed in alcohol for dissection and microscopic study, to de- 

 termine precisely the objects preferred by them for food. These were 

 examine<l at a later date, and all contents of the intestines were mounted 

 entire as microscopic slides, and permanently preserved. A careful 

 study was of course made of the organisms of the lake, as shown by 

 the product of the towing net, and when the experiment was finally 

 ended an equally careful examination followed of the living contents 

 of the water of the tank at that time. 



These fishes, like those previously described, had already reached 

 the age and condition at which it is customary to "plant" them in the 

 lake. The ventrals were still undeveloped, the egg-sac had nearly dis- 

 appeared, the four mandibular teeth were piesent, and the median fin 



