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 (Eho, 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 the Pulmonata, 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 lame 

 dimensions attained by 

 this part of the ento- 

 derm is evident from 

 Figs. 78-83, pp. 177-185, 

 depicting the embryos 

 of Planorbis, HelLr and 

 Li max. The entoderm- 

 cells in other parts, 

 however, remain small, 

 especially ventral h- and 

 posteriorly, and these 

 j>arts give rise to the 

 posterior portion of the 

 intestine winch takes the course already described. The small- 

 celled portion of the entoderm spreads out further at a later 



I'n.. 92.— .4 and B, embryos of BytMnia tentaculata 

 at different stages (after v. Erlanger). a, anus ; 

 eg, cerebral ganglion ; /, foot ; 1*1. posterior lobe of 

 the liver ; m . mouth ; mes, mesoderm ; nig, stomach ; 

 //. rudiment of the kidney; op, operculum; p, peri- 

 cardial sac; /«>, pericardium; r, radular sac; s, 

 shell; t, tentacle ; v, velum; /•/. anterior hepatic 

 sac. 



