J 921.] N. Annandai<e & R. B. S. SewELI- : Vivipara, 235 



arise at the upper and posterior end. passing downwards to the 

 orifice through which the shell-gland opens into the uterus. At 

 this point the smooth ridge becomes continuous with a longitudi- 

 nal fold, which, as we shall see later, passes down the whole length 

 of the lower wall of the uterine cavit}'. I have throughout referred 

 to this U-shaped portion of the genital duct as the egg-shell gland. 

 In the earlier descriptions of T'. vivipara, such as that given by von 

 Siebold (1836 p. 244), it is referred to as a receptaculum seminis, 

 because free spermatozoa were found in the contents. That it 

 serves as a repository for semen is be3'ond doubt, but it seems to 

 me that its true active function is to produce the thin membranous 

 covering which surrounds the eggs. The egg-shell gland opens 

 below by a wide crescentic mouth into the thin-walled uterus. This 

 is a wide cavity, which we have alreadj'' seen lying on the right of 

 the mantle cavity throughout the whole length of the body-whorl. 

 It invariably contains eggs and developing 5-oung when once sexual 

 maturity has been reached. Running along the whole length of 

 the floor of the uterine cavity is a double fold of opaque-white 

 colour which is in marked contrast with the thin translucent 

 side walls This double fold has a narrow base of attachment 

 and the left-hand or inner fold is thin and convoluted while the 

 outer fold is thicker and has a straight margin. This outer fold is 

 covered with a ciliated epithelium and beneath this fold, between 

 it and the floor, the seminal fluid, which has been introduced by 

 the male is conducted up to the shell gland. The terminal portion 

 of the genital duct is comparatively narrow and thick-walled. 

 It opens on the right of the Vjranchial chamber by an oval orifice, 

 the vagina, which is situated terminally on a small papilla. 

 During copulation the right antenna of the male is introduced 

 through this orifice and the seminal fluid is deposited within the 

 uterus. 



The members of the genus Vivipara, as their name implies, 

 produce live young, but they are actually ovo-viviparous. If we 

 examine the contents of the uterus during the breeding season we 

 find that the lower region of the duct contains numerous joung, 

 with 2-g- turns in the shell, ready to be born, but as we pass 

 further and further upwards the state of maturity of the young 

 becomes less and less, until at the extreme upper end we find large 

 ova containing an extremely minute embryo, with only half a turn 

 in the spiral of the visceral hump. These eggs are large and are 

 pj'riform or globular in shape. They are surrounded by a thin 

 delicate memLrane. which at one point is twisted up and produced 

 into a kind of free pedicle. Filling the whole egg, and surround- 

 ing the young embryo is a mass of faintly blue albuminous ma- 

 terial, which under the higher powers of the microscope, can be seen 

 to contain large numbers of spermatozoa, so that it would appear 

 that the seminal fluid of the male serves the double function of 

 fertilizing the ovum and providing in part for the nourishment of 

 the embryo. In addition to the spermatozoa we flnd numerous 

 fine spicules which dissolve readily on the addition of glacial 



