[7J THE FIRST FOOD OF THE COMMON WHITEFISH. 777 



natural preference, since it was doubtless also more abundant in the 

 water containing them. 



More light was thrown upon the earliest food habits of these fishes 

 by the discovery of raptatorial teeth upou the lower jaw than by these 

 dissections of their alimentary canals. All the families of fishes which 

 I had previously studied, whose young were provided with teeth, were 

 found strictly dependent at first upon Entomostraca and the minuter 

 insect larvae ; while only those whose young were toothless fed to any 

 considerable extent upon other forms. The discovery of teeth in the 

 young whitefish, therefore, placed this species definitely in the groux) 

 of those carnivorous when young. The fact that the adult was itself 

 toothless interfered in no way with this inference, because other tooth- 

 less fishes (Dorsoma) whose young were furnished with teeth had been 

 found carnivorous at an early age. 



The inconclusive character of the results thus far obtained made it 

 necessary to attempt to imitate more closely the natural conditions of 

 the young when hatched in the lake. In February, 1881, I obtained, 

 through the kindness of Mr. Clarke, twenty-five specimens of living young 

 whitefish, saved from a lot which he was planting in the waters of Lake 

 Michigan, off Racine, Wis. I succeeded in conveying these to the labora- 

 tory without loss, and there kept them for several days in a glass aqua- 

 rium 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 vicinity. These consisted of many diatoms and filamentous fresh- 

 water Algse, of two or three species of Cyclops, of Canthocamptus illinoi- 

 sensis, and Diaptomus sanguineus among the Copepoda, and of two rather 

 large Cladocera, Simocephalus vetulus and S. americanus. These little 

 fishes were kept under careful observation for several days, the water 

 in the aquarium being frequently aerated by pouring. 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 Entomos- 

 traca (the Simocephalus, and even the Diaptomus) were quite beyond 

 the size and strength of these little fishes, and that only the smaller Co- 

 pepoda among the animals available could afford them any food at 

 first. These they followed about from the beginning with signs of 

 peculiar interest, occasionally making irresolute attempts to capture 

 them. Two days after their arrival, one of the young whitefish 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 atten- 

 tions 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 antedate the sen- 

 sation of hunger. On the 25th the fourteenth and last remaining fish 

 captured its Cyclops and was itself sacrificed in turn. As an indica- 

 tion of the efficiency of the raptatorial teeth, it may be worth while to 



