THE FORMATION OF THE ORGANS— THE GENITAL ORGANS. 219 



and begin to coil, but there is as yet no sexual differentiation sax, 

 that this increase in growth takes place at an earlier stage in the 

 male tliau iii the female. 



The male genital apparatus of PaliuHna is composed of the germ- 

 gland just described, 

 which becomes the 

 testis, of the efferent 



duct, which lias also 



been to some extent 

 described, ami of a 

 much longer section, 

 i he vas deferens ; the 

 latter, which leads to 

 the penis, develops in a 

 somewhat different way. 

 This part of the vas 

 deferens arises in the 

 form of a groove in the 

 hasc of the mantle- 

 cavity into which the 

 previously formed 

 (primary) efferent duct 

 "pens. The groove 

 closes and, in the form 

 of a tube, extends as far as the right tentacle where the penis 

 develops. 



In some Prosobranchs, this seminal groove is retained throughout life ami is 

 continued from the male genital aperture in the mantle-cavity to the tip of 

 the penis. We thus tiud here, as in the formation of the secondary ureter of 

 the Pulmonates, conditions which are permanent in other forms appearing as 

 consecutive ontogenetic stages. 



The female genital apparatus of Paludina does not develop as eai'ly 

 as that of the male. Whereas the chief features of the latter can 

 be recognised at the end of embryonic development, those of the 

 female cannot lie distinctly made out until several weeks after birth. 

 At this stage, the rudiments of the albumen-gland appear in the 

 form of eight to twelve tubular outgrowths near the point where the 

 ectodermal efferent duct unites with the germ-gland. The ovary is 

 still represented by a tube lined by undifferentiated epithelium. The 

 short tube which extends from the ovary to the albumen-gland is 

 said to he derived from the mesodermal rudiment, like the short piece 



Fig. 102.— Portion of a sagittal section of an embryo 

 of Paludina vivipara in a younger stage than thai 

 depicted in Fig. 100 (after v. ERLANGBR). "//, 

 efferent duet ; <l , intestine ; </. rudiment of the 

 genital gland; /. liver; tries, mesodermal tissue; 

 ////', mantle-cavity. 



