145 



I succeeded in conveying these to the laboratory without loss, and 

 there kept them for several days in a glass aquarium and supplied 

 them with an abundance of the living objects to be obtained by 

 drawing a fine muslin net through the stagnant pools of the vicin- 

 ity. These consisted of many diatoms and filamentous fresh-water 

 Algae, of two or three species of Cyclops, of Canthoc-impius ilUnuise-n- 

 sis, and Di'iptomus sang nine us among the Copepoda, and of two 

 rather large Ciadocera, Slniocephalns vetidus and *S'. amerlca)uis. 

 These little fishes were kept under careful observation for several 

 days, the water in the aquarium being frequently aerated by pour- 

 ing. Many of them had, however, been injured by handling, and 

 eleven of the specimens died without taking food. It was soon 

 evident that the larger Entomostraca (the Simocephalus, and even 

 the Diaptomus), were quite beyond the size and strength of these 

 little fishes, and that only the smaller Copepoda among the animals 

 available, could afford them any food at first. These they followed 

 about from the beginning with signs of peculiar interest, occasion- 

 ally making irresolute attempts to capture them. Two days after 

 their arrival, one of the young white-fish had evidently taken food, 

 which proved, on dissection, to be a small Cyclops. During the 

 next two days nine others began to eat, dividing their attentions 

 between the Cyclops above mentioned and the Canthocamptus, and 

 on the 22d two others took a Cyclops each and a third a Cantho- 

 camptus. One of these fishes contained still a large remnant of 

 the egg-sac, showing that the propensity to capture prey must an- 

 tedate the sensation of hunger. .On the 25th the fourteenth and last 

 remaining fish captured its Cyclops and was itself sacrificed in turn. 

 As an indication of the efficiency of the raptatorial teeth, it may 

 be worth while to note that I saw one of the smallest fishes make 

 a spring at a Cyclops, catch it, give three or four violent wriggles, 

 and drop it dead to the bottom 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 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 occurring 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 conditions. 

 Through the generosity of the Exposition company, of Chicago, I 

 was allowed the use of one of the large aquarium tanks in the ex- 

 position building on the lake shore, and by the repeated kindness 

 of Mr. Clark, of Novthville, 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 chang- 

 ing cars at intermediate points, about two thirds of these were dead 

 when they reached my hands. Those living were immediately trans- 

 ferred 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 



F. C— 10 



