198 Heredity. . 



Xiphophorus Hellerini, the inferior margin of the anal 

 fin is developed into a long filament which 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 Callionymus the males while 

 young resemble in color and structure the adult fe- 

 males." 



Darwin discusses the question whether, when the male 

 differs in a marked manner from the female in color or in 

 other ornaments, he alone has been modified with the va- 

 riations inherited only by his male offspring, or whether 

 the female has been specially modified and rendered in- 

 conspicuous for the sake of protection, and he con- 

 cludes that with most fishes in ivhich the sexes differ in 

 color or in other ornamental characters, the males origi- 

 nally varied. 



LIZARDS. Among lizards the sexes often differ 

 greatly in various external characters, and the male sex 

 is in almost every case the one which is peculiar. Among 

 the many examples given by Darwin I quote the follow- 

 ing: 



"In Anolis cristatellus the male is furnished with a 

 crest which runs along the back and tail and can be 

 erected at pleasure, but of this crest the female does not 

 exhibit a trace, although in other species the female does 

 have an imperfect crest, which is much less developed 

 than it is in the male. In the genus Sitana the males 

 alone are furnished with a large throat pouch, which can 

 be folded up like a fan, and is colored blue, black and 

 red during the pairing season. The female does not 

 possess even a rudiment of this appendage. The male of 

 Ceratophora aspera has a long appendage half as long as 

 his head on the tip of his snout. In a second species of 

 the same genus a terminal scale forms a minute horn on 



