The Organs of Reproduction 129 



backs (Gasterosteidce), a group in which the male fish, though 

 a pygmy in size, is very fierce in disposition. 



In a minnow of Europe (Rhodeus amarus) the female is said 

 to deposit her eggs within the shells of river mussels. 



Sexual Modification. In the relatively few cases in which 

 the sexes are unlike the male is usually the brighter in color 

 and with more highly developed fins. Blue, red, black, and 

 silvery-white pigment are especially characteristic of the male, 

 the olivaceous and mottled coloration of the female. Sometimes 

 the male has a larger mouth, or better developed crests, barbels, 

 or other appendages. In some species the pattern of coloration 

 in the two sexes is essentially different. 



In various species the male develops peculiar structures not 

 found in the female, and often without any visible purpose. In 

 the chimaera a peculiar cartilaginous hook armed with a brush 

 of enamelled teeth at the tip is developed on the forehead in the 

 male only. In the skates or true rays (Raja) the pectoral fin 

 has near its edge two rows of stout incurved spines. These the 

 female lacks. In the breeding season, among certain fishes, the 

 male sometimes becomes much brighter by the accumulation of 

 bright red or blue pigment accompanied by black or white pig- 

 ment cells. This is especially true in the minnows (Notropis] , the 

 darters (Etheostoma) , and other fresh- water species which 

 spawn in the brooks of northern regions in the spring. In the 

 minnows and suckers horny excrescences are also developed 

 on head, body, or fins, to be lost after the deposition of the 

 spawn. 



In the salmon, especially those of the Pacific, the adult male 

 becomes greatly distorted in the spawning season, the jaws and 

 teeth being greatly elongated and hooked or twisted so that the 

 fish cannot shut its mouth. The Atlantic salmon and the trout 

 show also some elongation of the jaws, but not to the same 

 extent. 



In those fishes which pair the relation seems not to be per- 

 manent, nor is there anything to be called personal affection 

 among them so far as the writer has noticed. 



There is no evidence that the bright colors or nuptial adorn- 

 ments of the males are enhanced by sexual selection. In most 

 species the males deposit the sperm -cells in spawning-grounds 



