THE DEVELOPMENT OP xYPLYBIA PUNCUATA. 



519 



network enclosing- uniform small vacuoles which never contain 

 yolk. The nuclei are not very different in appearance from 

 those of the stomach wall, but ai-e usually larger in size. Ex- 

 ternally it is clothed with a thin epithelium. The right liver 

 undergoes no apparent change when the larva emerges from 

 its capsule. It is presumably always secretory in function. 



Our account of the development of the liver differs from 

 that of Mazzarelli, for he states that the right and left liver 

 arise each from one of the two large endomeres, and this we 



Text-fig. 8. 



K 1. 



LV 



K2 



Diagrammatic view of an embiyo at a stage when the large 

 retractor muscle is first formed ; seen from the dorsal surface. 

 F. Foot. XL Primitive kidney. K2. Secondary kidney. i.L 

 Left liver. M. mouth. Ot. Otocyst. St. Stomach. 



have shown to be incorrect. The peculiar mode of formation 

 of the left liver is evidently correlated with the great size of 

 the endomeres. All the yolk is contained within them, 

 whereas, in such a form as Fiona, certain cells of the anterior 

 portion of the stomach wall derived from 46- are heavily 

 laden with yolk and become gradually evagiuated to form 

 the liver. This mode of formation of the liver in Fiona is, in 

 fact, not unlike that of the right liver in Aplysia, but the 

 latter, as we have pointed out, never contains yolk. 



The large liver is very characteristic of Opisthobranch and 



