PHENOMENA OF SEX 309 



male Chimsera an anterior portion of each pelvic fin is separated 

 from the rest and provided with two large dermal spines. The 

 most peculiar organ, however, is a knobbed process covered with 

 spines situated on the middle of the head a little in front of the 

 eyes. The organ, known as the frontal clasper, is directed for- 

 wards and below it is a depression into which it is lowered 

 when not in use. Professor Bashford Dean found on females 

 of Chimcsra colliei taken off the coast of California, very distinct 

 marks and scratches on the skin at the base of the dorsal fin, 

 and believes that these were caused by the frontal clasper of the 

 male, which probably curls its body about that of the female 

 and inserts the spines of its clasper into her skin in the position 

 described. Harriotta, which has been taken in the North 

 Atlantic at depths of 707 to 108 1 fathoms, has no frontal 

 clasper, and the posterior claspers are small and rudimentary ; 

 it has been suggested that the eggs in this genus are fertilised 

 after extrusion. In Callorhynchus of the South Pacific the 

 organs are similar to those of Chimaera. 



In the Dipnoi or lung-fishes there is one peculiar character 

 confined to the males in the South American Lepidosiren : the 

 pelvic fins are covered in the breeding season with processes of 

 bright red colour from the numerous blood-vessels they contain. 

 The use of these structures is discussed in the section on breed- 

 ing habits. 



In the North American Bow-fin {Amid) among the living 

 Holostei the male is distinguished by its smaller size and by a 

 black spot at the base of the caudal fin. 



In the male salmon during the breeding season the anterior 

 end of the lower jaw grows into a large hook-like process which 

 is turned vertically upwards and when the jaws are closed occu- 

 pies a deep cavity between the primaxillary bones of the upper 

 jaw. This process serves as a weapon in the fights of the male 

 salmon, which make violent charges at each other. It is a 

 well-known fact that in fishes the males are usually smaller 

 than the females, and Darwin remarks that as in many kinds 

 of fish the males habitually fight together it is surprising that 

 they have not generally become larger and stronger than the 

 females through the effects of sexual selection. It is probable, 

 however, that in those cases in which the males have the 

 habit of fighting they are really larger than the females. It 



