202 



SEXUAL DIMORPHISM 



green. On the ventral surface, the throat, the lower side of 

 the pelvics, and the ventral fin acquire some black pigment, 

 the ventral occasionally showing a bluish tinge in addition. 

 The colour change in the eye seems to be limited to the 

 breeding season. The other colours are more permanent, but 

 their brilliance, especially that of the yellow, is much more 

 intense during the breeding season. It was found that the 

 special coloration of the male was much more directly con- 

 nected with the maturity of the genital organs than the 

 structural differentiation. The smallest sexually mature male 

 was 6| inches long, and had the blue and yellow coloration 

 well, though not completely, developed, and the structural 

 peculiarities well marked. A larger but sexually immature 

 male, 7^- inches long, although its dorsal fin was much elon- 

 gated, showed none of the special coloration. The male is 

 distinctly larger than the female, being stated to reach a 

 length of 1 foot (30 cm.), while the female does not reach 10 

 inches (25 cm.). The difference in size is partly due to the 

 greater length of the snout and caudal fin in the male. 



Mr. Holt's observations were made upon specimens living 

 in a glass-fronted tank, of which the bottom was covered 

 with fine light-coloured gravel. A number of females and 

 small undifferentiated males were living in this tank in the 

 winter of 1897-98, and two fine fully developed males were 

 introduced in January 1898. Until February 11, all the 

 dragonets were quiet in their movements, and the adult 

 males were not observed to display their dorsal fins. On the 

 date mentioned, and every following day till February 19, 

 the pairing repeatedly occurred. When it was going on all 

 the dragonets gave signs of unusual excitement, but the chief 

 actors were the two adult males. These kept darting along 

 the bottom of the tank at short intervals, at the same time 

 displaying their special characters. The dorsal fins were 

 erected sometimes before the fish made its rush, oftener at 



