62 



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 determine precisely the objects preferred 

 by them for food. These were examined 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, it was followed by an equally careful examination 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 disappeared, the four mandibular teeth 

 were present, and the median fin extended from the tips of the 

 pectorals on the belly to a point opposite the middle of the 

 same fins on the back. In most the egg-sac did not protrude 

 externally, being reduced in some to a droplet of oil, but remain- 

 ing in a few of a size at least as great as that of the head. The 

 alimentary canal was, of course, a simple, straight tube, without 

 any distinction of stomach and intestines. 



The sufferings of these fry in transit had doubtless weakened 

 the vitality of the survivors, and although every care was taken 

 to keep the water of the tank fresh and pure, about one-third of 

 those remaining died during the progress of the experiment. 

 The aquarium in which they were confined was built of glass, 

 and had a capacity of about one hundred cubic feet. The tem- 

 perature, tried repeatedly, stood at forty-two Fahrenheit. A 

 steady current of the water of the lake was maintained through 

 this tank, entering through a rose, from which it fell in a spray, 

 thus insuring perfect aeration. 



By far the greater part of the organic contents of the water 

 of the lake, as shown by the product of the towing-net, con- 

 sisted of diatoms in immense variety, which formed always a 



