SPAWNING BEHAVIOR IN FUNDULUS HETEROCLITUS. 339 



retreats to a convenient hiding place, there to recuperate for 

 another series of encounters. Several other fairly brilliant males 

 could be made out, hiding in the same fashion. The females are 

 still too frightened to emerge from shelter. The fierce aspect of 

 these fighting males is remarkable in creatures so small. When 

 swimming ordinarily the dorsal fin is not used, being kept folded 

 flat on the back. But whenever fighting or sexually excited, this 

 fin comes into action, expanding like a bat-wing sail. 



The reckless courage of the ruling male surprised me. I put 

 into the aquarium a male Fundnlns hereroclitns of large size. 

 Without a moment's hesitation the little warrior dashed up to the 

 far bulkier intruder and caused the latter to beat an ignominious 

 retreat. Several larger fish of other species met a similar recep- 

 tion and fate. 



July 2?. On the following day the ruling male had been de- 

 posed and there was an extremely vigorous struggle for suprem- 

 acy among the other males. Only one of these failed to enter 

 the lists. This one had as yet not reached the sexual climax and 

 was, consequently Jwrs dn combat. As one might have antici- 

 pated, the male that had ousted the original ruling male was the 

 victor, the others finally acknowledging defeat by retiring to 

 shelter. The same program was then repeated that has been 

 described for the previous days. 



The deposed male now showed signs of waning vigor in the 

 paling of his " plumage," which was becoming rather dull at the 

 posterior end of his body. This fading out of brilliancy pro- 

 ceeds in a postero-anterior direction, the top of the head being 

 the last part of the body to lose its bright coloration. 



July 29. Both males and females of Cyprinodon are seen to 

 have passed the sexual period. The females are no longer dis- 

 tended and no longer show any fear of the males, the two sexes 

 mingling quite amicably. The males have all lost their spawning 

 coloration except for traces of iridescent green about the head. 

 The dorsal fin of the males, having lost most of its pigment, 

 shows in one or two cases quite a noticeable dark spot on the 

 posterior rays. This spot is, however, not nearly so distinct as 

 that in the females. In color the males are now pale green with 

 dusky markings that stand out somewhat more clearly now that 



