452 GERTRUDE MAREAN WHITE 



for fishes. The results of feeding experiments are strongly in- 

 dicative of a color sense. On the other hand, Hess contends 

 that fishes see colors as shades of gray, as a totally color-blind 

 human being perceives them. 



CONDITIONS OF EXPERIMENTATION 



The mudminnows and sticklebacks used in the experiments 

 to be described in this paper were obtained from Lake Wingra 

 and Lake Mendota, near Madison, Wisconsin. They were not 

 kept in running water, since it was found that they thrived 

 equally well without it, provided the water was changed from 

 one to three times a week. City water was used because t is 

 drawn from an artesian well and contains few organisms inju- 

 rious to fishes. Individuals were kept in separate jars and care- 

 fully observed, as many experiments as possible being per- 

 formed upon each fish. One mudminnow which is still alive has 

 been under observation over three years. 



When first introduced into aquaria the fishes were left undis- 

 turbed for something like a week, except for changing the water. 

 They commonly refused to eat during this period of adjustment; 

 usually some died at first, but thereafter few were lost. By the 

 end of a w^eek the survivors were likely to be hungry and suffi- 

 ciently accustomed to the presence of persons in the room to eat 

 bits of food dropped into the water. Shortly after this they 

 could generally be induced to take food at the surface, and after 

 several days to jump out of the water for food. It was neces- 

 sary to estimate carefully the amount of food to be given, as the 

 fishes have a tendency to consume large quantities at one time 

 and then fast for several days. In most cases feeding was car- 

 ried on in the laboratory from one to three months before ex- 

 periments were begun, or until the fishes had formed the habit 

 of taking food daily. 



Although the following observations were made especially 

 on the mudminnow, they apparently apply to the stickleback 

 as well. In making selection for training experiments, marked 

 differences in the adaptability of fishes of different ages were 

 found. Whereas mature mudminnows spend most of the time 



