ASSOCIATION AND COLOR DISCRIMINATION 455 



Twenty fishes (all young fry— Ij to If inches — except one) 

 were observed during an entire night in November from 10:30 

 P.M. until 7:30 a.m. The vessels containing them were placed 

 on tables where there was only enough illumination to faintly 

 discern the outlines of the fishes. The position of each fish 

 was noted every half hour, also whether it was active or at rest. 

 Of 201 observations made, the fishes were in 124 instances near 

 the surface, and in 77 instances the fishes rested on or near the 

 bottom. At daybreak nearly all the fishes were moving about 

 actively. Likewise, nineteen fishes were observed at half-hour 

 intervals during one afternoon and evening. From all these 

 observations it was concluded that mudminnows, while only 

 slightly less active at night than during the day, exhibit some- 

 what greater activity at daybreak. Although very young in- 

 dividuals came to rest anywhere in the dish, they spent rela- 

 tively more time at the surface than on the bottom, whereas 

 older individuals evinced a preference for the botton. Protec- 

 tive adaptation would seem to cause the young fry to stay at the 

 surface, since the large fishes which are their natural enemies 

 are usually found near the bottom. 



SENSE ORGANS USED IN SEEKING FOOD 



In these fishes the senses of sight and smell are most used in 

 seeking food. The stickleback displays more alertness in using 

 both senses and much higher degree of acuteness of the olfactory 

 sense. The method used by Parker ('11) in testing the olfactory 

 sense of fishes was tried with both mudminnows and stickle- 

 backs. Cloth packets, one of which contained meat and the 

 other cotton, were suspended at opposite ends of the aquarium. 

 The mudminnows did not show that they perceived either 

 packet though they swam in close proximity to both. 



The sticklebacks behaved difTerently. The appearance of the 

 packets attracted them at once. Those fishes which went to- 

 wards the packet containing meat darted furiously upon it and 

 pulled at it with great excitement, but those which swam in the 

 direction of the packet of cotton in most cases stopped about 

 4 cm. away and turned off sharply in another direction. Only 



