SPAWNING BEHAVIOR IN FUNDULUS HETEROCLITUS. 321 



the aquarium and put him in a smaller vessel by himself, being 

 careful to keep him out of the strong light. When thus removed 

 from the sexual environment, he almost immediately underwent 

 a very marked change in appearance, becoming decidedly lighter 

 in color, and inside of ten minutes losing all of the steely blue 

 glint that is so characteristic of sexual excitement. Putting a 

 dark colored fish in a strong light causes a similar lightening of 

 color, but that the change in question was not due to light seems 

 certain for all strong light was excluded. As soon as this ruling 

 male had been removed the other males usurped his prerogative 

 and a struggle for supremacy immediately ensued. The combat 

 between the six remaining active males was for a time very evenly 

 waged, since there was no great disparity in size, but after about 

 ten minutes a single male, and he not the largest, had gained 

 supremacy and had succeeded in driving away his rivals when- 

 ever they approached. Occasionally one of the outsiders plucked 

 up sufficient courage to challenge the ruling male and a combat 

 ensued. The males fight with their heads and mouths, butting 

 one another fiercely and accasionally locking jaws and struggling 

 like dogs. When a male wishes to challenge he approaches 

 rather cautiously, body trembling with excitement and all fins 

 extended to the utmost, presenting as formidable an aspect as 

 possible. The male thus challenged adopts a similar attitude 

 and rushes at his foe with alacrity. Curiously enough the male 

 that has once gained supremacy always emerges victorious from 

 these contests, and the defeated male retires into hiding until he 

 has regained sufficient courage to challenge again. After about 

 half an hour the large male that had been removed to another 

 vessel was returned to the aquarium. At first he seemed to take 

 no interest in the spawning activity going on about him, but 

 gradually he aroused himself and made an occasional half-hearted 

 attempt to clasp a female that came near him and advertized by 

 her attitude her desire to spawn, but he was always rudely inter- 

 rupted and put to rout by the new ruling male, which although 

 of very much smaller size, attacked with such vigor that his much 

 bulkier opponent was forced to retire. By degrees, however, 

 the large male increased in vigor, at the same time growing 

 darker and reassuming the blue glint that he had so quickly 



