104 
The First Food of the Common White-Fish. 
on these fourteen fishes, we may say that eight of them ate a sin- 
gle Cyclops each, that one took two, and another three of the 
same, that one took a single Canthocamptus, that two specimens 
captured two each of this genus, and that finally, a single fish ate 
Cyclops and Canthocamptus both. The final conclusion was a 
highly probable inference that the smallest Entomostraca occur- 
ring in the lake would prove to be the natural first food of the 
species. 
In order to test this conclusion with precision, I arranged a sim- 
ilar,, experiment on a larger scale and under more natural condi- 
ditions. 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 ville, Michigan, 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 temperature 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 upon the remotest breakwaters, immense numbers of all 
organic objects in the water were easily obtained. After enclosing 
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 descrip- 
tions indiscriminately into the water from day to day, thus keep- 
ing 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 determine pre- 
cisely the objects preferred by them for food. These were ex- 
amined at a later date, and all contents of the intestines were 
mounted entire as microscopic slides, and pemanently 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 experi- 
