204 



GASTROPODA. 



the different forms, but generally appear to open into the stomach at 

 its postero-ventral end, so that a relation between the nutritive sacs 

 and the liver seems probable. As the liver continues to develop, the 

 sacs decrease in size. 



The two entodermal stomach-diverticula of different sizes are, as 

 already mentioned, also found in the larvae of the Opisthobranchia 

 (Fig. 72, di, p. 162). They are here said to belong rather to the 

 dorsal and anterior part of the stomach (Rno, No. 93 ; FISCHER, 

 No. 30). According to FISCHER, they become transformed direct 

 into the liver, forming the outgrowths which enter the dorsal 



papillae (cerata). The 

 left diverticulum yields 

 the principal lobe of 

 the liver, while the 

 right, in the Nudi- 

 branchia, is of small 

 size. 



In thePulmonata,the 

 position of the nutritive 

 ^ masses is somewhat 



different. It has been 

 asserted that, in them, 

 the principal mass of 

 large cells filled with 

 albumen lies at the 

 dorsal side. The large 

 dimensions attained by 

 this part of the ento- 

 derm is evident from 

 Figs. 78-83, pp. 177-1 85, 

 depicting the embryos 

 of Planorbis, Helix and 

 Liinax. The entoderm- 



FIG. 92. A and B, embryos of Bythinia tentaculata cells in other parts, 



at different stages (after v. ERLANGER). a, anus ; u owpvp , rprna in small 



eg, cerebral ganglion ; /, foot ; hi, posterior lobe of lowev er > r 

 the liver ; m, mouth ; mes, mesoderm ; mg, stomach ; 



especially ventrally and 

 posteriorly, and these 

 parts give rise to the 

 posterior portion of the 



intestine which takes the course already described. The small- 

 celled portion of the entoderm spreads out further at a later 



n, rudiment of the kidney ; op, operculum ; p, peri- 

 cardial sac ; pe, pericardium ; r, radular sac ; s, 

 shell ; t, tentacle ; v, velum ; vt, anterior hepatic 

 sac. 



