296 A HISTORY OF FISHES 



Ray {Raia clavata) the teeth of the male are quite unHke those 

 of the female, although alike in immature individuals of both 

 sexes {cf. p. 127). 



Among Bony Fishes intromittent organs [i.e. organs for 

 introducing the spermatozoa into the body of the female) 

 naturally occur only in those fishes in which fertilisation of 

 the eggs is internal. A simple organ of this nature is provided 

 by the prolongation of the genital or urino-genital orifice to 

 form a conical papilla or a more or less lengthy tube. In some 

 of the Toothed Carps or Cyprinodonts (Cyprinodontidae) the duct 

 from the male reproductive organ is produced as a tube to 

 the end of the anterior rays of the anal fin, and in the Four-eyed 

 Fish (Anableps) this tube is covered w^ith scales (Fig. 740). The 

 genital aperture of the female Four-eyed Fish is covered by a 

 special scale, the foricula, which is free on one side but not on 

 the other. In some individuals the opening beneath the scale 

 is on the right side, in others on the left, while among the males 

 some have the intromittent organ turned towards the right, some 

 towards the opposite side. Thus, in order to transfer the milt to 

 the genital duct of the female, copulation takes place sideways, 

 and it is necessary for a right-sided male to pair with a left-sided 

 female and vice versa. 



In many South American and Central American Cyprino- 

 donts (sub-family Poeciliinae) the males are provided with com- 

 plicated intromittent organs developed in connection with the 

 anal fin, which in these fi.shes is much modified and placed 

 farther forward than usual. The third, fourth, and fifth rays 

 of the fin are enlarged and produced, forming the margin of 

 a groove or closed tube into which the genital duct opens. 

 The rays may end in curved hooks, spines, or barbs, the function 

 of which seems to be connected with keeping the organ in 

 position during copulation. The whole organ is freely movable, 

 and is supported internally by bony processes. The genital 

 aperture is placed just in front of the base of the anal fin, and 

 may be covered by the pelvic fins, which take part in conveying 

 the seminal fluid into the groove. Another type of Cyprinodont 

 (Phallostethinae) , ranging from the Malay Peninsula to the 

 Phihppines, is remarkable for the possession by the male of a 

 large fleshy appendage known as the priapium, which is 

 situated below the head and chest. This appendage has a 

 complicated internal skeleton of its own, and contains not only 

 the ducts from the kidneys and reproductive organs, but also 

 the terminal parts and openings of the intestine. In addition, 



