BREEDING HABITS OF RAINBOW DARTER. 55 



through the water and affect the lateral line organs of the female. 

 In any case it appears that mechanical stimulation forms the chief 

 element in the behavior of the male toward the female while atti- 

 tudes especially suited to display his colors are less evidently 

 used. 



Between the males color displays are frequent. If two bril- 

 liant males are rivals and of the same size they pose side by side 

 with their first dorsals elevated. If one of the two fishes is a 

 small male he does not pose, but after elevating his first dorsal 

 flees. This display by the small male appears to serve as a sex 

 recognition character by which the other males distinguish him 

 from the females. Displays of force also take place between 

 brilliant males. These consist of blows delivered by the tail or 

 head of one male against the side of the other. Or they consist 

 of sham struggles during which the fish swim about side by side. 

 While thus swimming the first dorsal fin is always raised and 

 each of the two fish makes use of the same vibratory movement 

 of the head that is used toward the female. The net result of 

 these displays of color and force between males is in the majority 

 of cases to exclude the smaller males from participation in pair- 

 ing. They appear to have, however, a further effect ; that of 

 raising the general state of excitation among the males. H. E. 

 Zeigler is quoted by Gross (1896) as expressing the belief that a 

 high state of nervous excitement is necessary for the pairing of 

 all animals. Hacker (1900) has applied this interpretation to the 

 displays of color and movement of male birds during the mating 

 season. He believes that they serve to overcome the coyness of 

 the female and to bring her into the physiological state necessary 

 for pairing. The same interpretation seems to apply to the breed- 

 ing behavior of the male Etheostoma. Were the displays of color 

 and of force of the individual male merely random, not manifestly 

 adjusted to a female in one case and to a male in another case, then 

 they might be interpreted as the meaningless result of nervous 

 excitation. But since they are exactly adjusted I conclude that 

 they have, in addition to their function of limiting the breeding 

 activities of the smaller males, a further definite function ; that of 

 raising the general state of excitation among all the participating 

 fishes. 



