SEXUAL CH.\RACTERS — ELASMOBRANCH FISHES 



219 



is contracted this is not seen, but by a muscular movement the 

 web can be expanded as in the lower inset, in which case the claw 

 protrudes, and serves to prevent elision of the clasper from the 

 oviduct. 



Fig. 21 Rhinobatus productus. CI. Gl., clasper gland; S., siphon; S. Ap., 

 aperture of siphon tube; A., apopyle; H., hypopyle; P. F., pelvic fin; CI. T. 

 clasper tube; <SZ., slit; Rh., rhipidion;<S«., sentina; CL, ciaw. 



The clasper gland, w^hile conforming to the general type as in 

 Raia, Torpedo, etc., is the one which presents the niost mmor 

 differences. It is elongated and extremely narrow, and more 

 twisted out of one plane than the others. So small is its diameter 

 and so small the gland components that it is possible to cut 

 through two papillae in a transverse section (fig. 22) . The origin 

 of the groove, which ultimately becomes the siphon tube, is 

 unusually far forward in position. 



