382 THE DESCENT OF MAN. 



dorsal fin. Mr. W. Saville Kent remarks that this " sin- 

 gular appendage appears from my observations of the 

 species in confinement to be subservient to the same end 

 as the wattles, crests and other abnormal adjuncts of the 

 male in gallinaceous birds for the purpose of fascinating 

 their mates."* The young males resemble the adult 

 females in structure and color. Throughout the genus 

 Callionymusf the male is generally much more brightly 

 spotted than the female, and in several species, not only 

 the dorsal, but the anal fin is much elongated in the males. 



The male of the Coitus scorpius, or sea-scorpion, is 

 slenderer and smaller than the female. There is also a 

 great difference in color between them. It is difficult, as 

 Mr. LloydJ remarks, " for any one who has not seen this 

 fish during the spawning season when its hues are brighest 

 to conceive the admixture of brilliant colors with which it, 

 in other respects so ill-favored, is at that time adorned." 

 Both sexes of the Labmis mixtus, although very different 

 in color, are beautiful; the male being orange with bright 

 blue stripes and the female bright red with some black 

 spots on the back. 



In the very distinct family of the Cyprinodontidae 

 inhabitants of the fresh waters of foreign lands the sexes 

 sometimes differ much in various characters. In the male 

 of the Mollienesia petenensis, the dorsal fin is greatly de- 

 veloped 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 irregu- 

 larly 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 Xipliophorus Hellerii (fig. 

 30), the inferior margin of the caudal fin is developed into 

 a long filament, which, as I hear from Dr. Giinther, is 

 striped with bright colors. This filament does not contain 

 any muscles, and apparently cannot be of any direct use to 

 the fish. As in the case of the Callionymus, the males 



* "Nature," July, 1873, p. 264. 



f " Catalogue of Acantli. Fishes in the British Museum," by Dr. 

 Gilnther, 161, pp. 138-151. 



\ " Game Birds of Sweden," etc., 1867, p. 466. 



With respect to this and the following species I am indebted to 

 Dr. Giinther for information; see also his paper on the "Fishes of 

 Central America," in "Transact. Zoolog. Soc.," vol. vi, 1868, "p. 485. 



