Chap. XII.] FISHES. 9 



ally much more brightly spotted than the female, and in 

 several species, not only the dorsal, but the anal fin of the 

 male, is much elongated. 



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

 more slender and smaller than the female. There is also 

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

 as Mr. Lloyd 13 remarks, " for any one, who has not seen 

 this fish during the spawning-season, when its hues are 

 brightest, 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 Ldbrus mixtus, al- 

 though 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 Cyprinodontidse — • 

 inhabitants of the fresh waters of foreign lands — the sexes 

 sometimes differ much in various characters. In the male 

 of the Mollienesia petenensis, 1 * the dorsal fin is greatly 

 developed, and is marked with a row of large, round, ocel- 

 lated, bright-colored spots ; while the same fin in the fe- 

 male 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 Xiphophorus 

 Hellerii (Fig. 29), the inferior margin of the anal fin is 

 developed into a long filament, which is striped, as I hear 

 from Dr. Giinther, 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 while young resemble in color and structure the 

 adult females. Sexual differences such as these may be 



13 ' Game Birds of Sweden,' etc., 1867, p. 466. 



14 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. 



