THK FORMATION OF THK OIUiANS THK (JKNITAI, OKCANS. 219 



and begin to coil, but there is as yet no sexual different iat ion sa\e 

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

 male than in the female. 



The male genital apparatus of 1'nJinliim. is composed of the -vim 

 gland just described, 

 which becomes the 



testis, of the efferent 

 duct, which has also 

 been to some extent 

 described, and of a 

 much longer section, 

 t he vas defereus : the 

 latter, which leads to 

 the penis, develops in a 

 somewhat different way. 

 This part of the vas 

 deferens arises in t Ill- 

 form of a groove in the 

 base of the mantle- 

 cavity into which the 

 previously formed 

 (primary) efferent duct 

 opens. Tin? groove 

 closes and. in the form 

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

 develops. 



In some I'msnbranelis, ihis seminal groove is retained throughout life and is 

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

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

 i he I'ulimniates, conditions which are permanent in other forms appearing us 

 consecutive ontogenetic stages. 



The female genital apparatus of /W/////W does not develop as early 

 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 canimt be 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 be derived from the mesodermal rudiment, like the short piece 



Fn:. 102. Portion of a .sagittal .section of an embryo 

 of I 'nl n<l in <i i- i r i /in HI in a younger stage than that 

 depicted in Fig. 100 (after v. KULANUKK). it;/, 

 i-fferei.t dur-.t ; </, intestine ; //. rudiment of the 

 genital gland; /. liver; ///>'*, mesodermal tissue; 

 mil , mantle-cavity . 



