The Evidence from Sexual Characters. 197 



ficient to show that these animals follow the rule which 

 prevails in so many other groups of the animal kingdom; 

 that the males are more modified than the females; that 

 the males of allied species differ more than the females, 

 and that the mature male differs more than the mature 

 female from the young. 



In many species the male alone is ornamented with 

 bright colors, and lie is sometimes provided with curious 

 appendages which do not appear to be of any use what- 

 ever for the ordinary purposes of life. When the male 

 Callionymus lyra is freshly captured the body is colored 

 with various shades of yellow, with stripes and spots of 

 vivid blue on the head; the dorsal fins are pale brown, 

 with dark longitudinal bands, while the other fins are 

 bluish black; the female fish is of a dingy reddish 

 brown, with the dorsal fin brown and the others white. 

 The sexes differ in many other respects, and the dorsal 

 fin of the male is remarkably and excessively elongated. 

 The sexes are so different from each other that they were 

 for a long time regarded as distinct species, and the 

 male is known as the gorgeous dragonct, the female as 

 the sordid dragonet. 



The males of the various species of this genus differ 

 from each other in these sexual characters, and the young 

 males resemble the adult females in structure and color. 



The following extract from Darwin shows how greatly 

 the males of closely allied species differ from each other: 

 "In the male of the Mollienesia petenensis the dorsal fin 

 is greatly developed and is marked with a row of large, 

 round, ocellated bright-colored spots, while the same fin 

 in the female is smaller, of a different shape and marked 

 only with irregularly curved brown spots. In the male 

 the basal margin of the anal fin is also a little produced 

 and dark colored. In the male of an allied form, the 



