THE ELASMOBRANCH FISHES 



309 



sac is small and its blood supply is lacking. There is therefore no passage of 

 nutriment from the villi of the female through the blood system on the yolk 

 sac. But the long strap-like villi (fig. 269b) enter the spiracle and supply 

 nutriment direct to the digestive tract, as can be demonstrated by opening up 

 the digestive tract of the embryo ( Alcock, 1892) . 



At their posterior terminus the two uteri in an immature female may be 

 separated from the cloaca by a mem])rane or hymen across the oviduct. The 

 relation of the hymen (in Torpedo) may be seen from figure 270 by Wida- 

 kowich (1908) . The median union of the right and left uteri is prolonged back- 

 ward toward the cloaca by the uterine septum {s.) and a fold on each side 

 separates the oviduct from the cloaca. During 

 pregnancy the uterus is filled with a fluid and the 

 apertures remain closed. 



In Elasmobranchs in which the shape of the 

 claspers of the male is flat, the openings into the 

 uteri are slit-shaped, and in those forms in which 

 the claspers of the male are provided with sharp 

 hooks the lining of the terminal part of the uterus 

 is thickened. 



Secondary Sexual Characters 



Fig. 270. Diagram to sliow 

 the hymen between oviduct 

 and cloaca. (From Widako- 

 wich.) 



cZ., cloaca; 7ii/., hymen; o.d., 

 oviduct; s., uterine septum. 



Barring the fact that the female may be slightly 

 larger than the male, the most important second- 

 ary character separating the sexes in the Elasmo- 

 branchs is the presence of claspers in the male. 

 These, as we have seen, are formed as modifica- 

 tions of the inner lobe of the pelvic fin. In types like Heptanchus maculatus 

 the claspers in immature specimens are relatively insignificant so that it is 

 often difficult upon casual examination to distinguish male from female. In 

 most other types, however, the claspers are well developed and in the rays 

 they may be of enormous size. 



In one immature specimen of Heptanchus supposed to be a male, in addition 

 to the rudimentary oviduct only one of the pelvic fins bore a clasper. The con- 

 dition of gynandromorphism, in which one side of the body is male, the other 

 female, has been found in insects and birds, and its occurrence in the Elasmo- 

 branchs has also been previously noted ( Vayssiere and Quintaret, 1915) . 



The mucous covering of the claspers is usually devoid of placoid scales and 

 is provided with a lubricant. Distally, as we have seen in a study of the skele- 

 ton, the claspers are provided with one or more terminal pieces. These by 

 muscular action may be erected at right angles to the main axis of the clasper. 



The claspers have long been known to function in uniting the male and 

 female in copulation. This process among the Selachians was early studied 

 byAgassiz (1871) who discovered that one (or both) of the claspers is inserted 



