312 FISHES 



of the males is much elongated and provided at the extremity 

 with little finger-like processes, but there is no tube running 

 down the fin from the genital aperture. In two species of 

 Gladarichthys, Philippi succeeded, by observations on specimens 

 kept in an aquarium, in discovering how the milt of the male 

 is introduced into the female duct in these cases. It is evident 

 that if the milt was liquid as in ordinary fishes it would be diffi- 

 cult to introduce it without the aid of a tubular intromittent 

 organ. Philippi observed that the male in copulation bent his 

 ventral fin round either to the left or right so that its extremity 

 pointed forward and somewhat to the dorsal side, and then 

 darted at the female, touching the genital aperture with the 

 processes at the extremity of his ventral fin. The contact was 

 only momentary, the impetus of the male carrying him onwards 

 beyond the female. It was impossible to see any milt passing 

 from one fish to the other in this proceeding, and it was evident 

 that the genital apertures of the two fishes were separated by 

 the whole length of the ventral fin of the male. By slight pres- 

 sure on a male fish lying on a glass slide Philippi found that 

 small lumps of milt were expelled which adhered to whatever 

 they touched. These masses were found to be composed of 

 spermatozoa surrounded by an adhesive liquid, and the testes 

 were full of such masses, which form what in other cases are 

 called spermatophores. It is evident then that some of these 

 spermatophores are ejected at the moment of contact of the 

 ventral fin with the female in the movement above described, 

 and that they are drawn into the female duct by some sucking 

 action. The formation of spermatophores thus prevents the 

 dispersal of the spermatozoa in the water. 



In other species, as in Jenynsia and the four-eyed fish Ana- 

 bleps, a closed tube continued from the genital duct runs down 

 the front of the elongated ventral fin of the male, so that the 

 spermatozoa are conducted directly to the female aperture, and 

 it is not known that spermatophores are formed in these cases. 

 Whether there is a tube on the modified fin or not, copulation 

 takes place sideways, and it is found that in a given fish it 

 always takes place on the same side. In Anableps there is a 

 kind of hinge in the middle of the fin on the side of which is a 

 fleshy tubercle. When this tubercle is on the right the fin bends 

 to the left, when it is on the left the bend is to the right. In 



