308 FISHES 



less, of frequent occurrence and of great interest. Among 

 characters peculiar to the males the following kinds may be dis- 

 tinguished : ( i ) organs directly concerned in the fertilisation of 

 the ova, usually intromittent organs for introducing the milt into 

 the body of the female ; (2) structural peculiarities for aiding the 

 union of the sexes ; (3) weapons used by the males in fighting 

 with one another ; (4) structures which may be displayed in 

 courtship, but which are of the nature of ornaments or ap- 

 pendages, not of mechanical use ; (5) peculiarities of colour. 



Intromittent organs in the male are necessarily confined to 

 those fishes in which fertilisation is internal. They are universal 

 in Elasmobranchs (sharks, dog-fishes and skates) and Chimae- 

 roids in both of which sub-classes they consist of outgrowths of 

 the posterior parts of the pelvic fins and have been incorrectly 

 called claspers. In the dog-fish, Scyllhun canicula, each of these 

 organs has a deep groove on the posterior and internal surface 

 leading to a deep glandular pit at the base of the organ ; in 

 copulation the two grooves are placed together, both organs 

 are inserted into the cloaca of the female and the seminal secre- 

 tion is conducted along the grooves. Among the skates 

 (Raiidae) there are other differences between the sexes besides 

 the claspers. In some species the teeth are different ; in the 

 common thornback, for example, the teeth of the adult male 

 are pointed and sharp, there are about forty transverse rows in 

 each jaw and the outer teeth are lozenge-shaped, the central 

 ones conical with the points turned inwards. In the female 

 the teeth are flat and smooth, arranged in oblique rows, the 

 central being larger than the lateral. In the young males the 

 teeth are flat as in the females. In the males of all the species 

 there is an area of large sharp spines on the dorsal side of each 

 wing or pectoral fin, and this is wanting in the females. These 

 may be used for holding the female or for fighting with other 

 males ; the latter employment seems most probable, as it is 

 difficult to understand how spines in such a position could be 

 used in coition, whereas if the males buffet one another with 

 their wings the spines would be effective weapons. Pennant 

 stated as long ago as 1776 that several males pursue one female. 



Male Chimaeroids possess in addition to the intromittent 

 organs, commonly but erroneously called posterior claspers, 

 organs of the second kind used for holding the female. In the 



