PHENOMENA OF SEX 311 



they swim vertically upwards side by side while shedding the 

 eggs and milt. In the Scald- fish the peculiarity of the male is 

 also the elongation of the anterior dorsal fin-rays and those of 

 the pelvic fin. In Con's julis also the male sexual characters 

 are larger size, elongation of fin-rays, and more brilliant 

 coloration. 



A very marked difference of coloration occurs in Labrus 

 mixtus, one of the British wrasses ; the male is yellow or orange 

 with longitudinal blue stripes, the female is red with three large 

 black spots on the hinder part of the back. Unfortunately the 

 habits of this species in the breeding season have not been ob- 

 served. 



In the majority of the species of the carp family (Cyprini- 

 dse) the males develop in the spawning season, hard, wart-like 

 tubercles on the skin, which disappear after that season is over. 

 It has been shown that these nuptial excrescences are used in 

 some species in the battles of the males, or in nest-building, 

 while in some two males hold the female between them, pres- 

 sing against her and against one another behind and beneath 

 her. In the armoured cat-fishes (Loricariidse) of South 

 America there are also great sexual differences between the 

 sexes, but the habits of these are not so well known, except 

 that they build nests. 



Among the toothed carps (Cyprinodontidae) sexual differ- 

 ences are naturally most developed in the viviparous species, 

 since in these the males and females play different parts in the 

 drama of courtship and sexual union. The males in such 

 species are smaller and more brightly coloured and also less 

 numerous. In a few cases there are sexual characters in the 

 males which are not directly connected with copulation ; in 

 Mollienisia petenensis the dorsal fin of the male is very greatly 

 enlarged and marked with ocelli, and in Xiphophorus hellerii the 

 ventral margin of the caudal fin is developed into a long filament. 

 The copulatory organ is formed by modification of the ventral 

 fin, which consists of few rays and is situated immediately be- 

 hind the anus and genital aperture. Erich Philippi of Berlin 

 has recently discovered a viviparous species, Characodon lateralis, 

 in which the ventral fin of the male is not modified, but is 

 similar to that of the female. In a number of other species 

 such as Gambusia, Mollienisia and Xip/iop/iorus, the ventral fin 



