The elasmobranch fishes (1934) The elasmobranch fishes elasmobranchfish03dani Year: 1934 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 a
The elasmobranch fishes (1934) The elasmobranch fishes elasmobranchfish03dani Year: 1934 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; , 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 im
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