THE GASTROPODA 



95 



glossa, viz. in Pleurotomaria (Fig. 127, sp.c\ Haliotis, the Turbinidae, 

 etc., and in Nassopsis and Chytra (which, according to Moore, possess 

 both the spiral caecum and the style-sac), but is simple and straight 

 in Ampullaria, a large number of Opisthobranchia, the Limacinidae, 

 the majority of the Cavoliniidae, Aplysia, several Doridomorpha (in 

 which it is rugose internally, and has incorrectly been described as 

 a "pancreas"), and finally in a number of Basommatophora, the 

 Limnaeidae, and various Planorbidae. 



The liver or digestive gland constitutes the essential organ of 

 digestion. It more or less completely surrounds the stomach, and is 



divided into lobes, the number 



ancl * orm of wnicl1 varv in 



Fia. 76. 



Philine aperta, dorsal aspect ; the body-wall is 

 supposed to be transparent, a, anus; a.g, ab- 

 dominal ganglion ; c.g, cerebral ganglion ; c.h, 

 cephalic hood ; y, gill ; g.o, genital (hermaphroditic) 

 orifice ; gz, gizzard ; h, heart ; in, intestine ; k, 

 kidney ; m, mouth ; m.p, masticatory plate ; os, 

 osphradinm ; pa, mantle ; par, parapodia (lateral 

 lobe of foot) ; p.g, pedal ganglion ; p.l, inferior 

 pallial lobe ; pl.g, pleural ganglion ; r.m, retractor 

 muscle of buccal mass ; r.o, renal opening ; r.p, 

 reno-pericardial opening ; s.g, seminal groove ; sh, 

 shell ; s.i, supra-intestinal ganglion ; st, stomach. 

 (After Guiart.) 



Alimentary canal of Eolis papil- 

 losa, dorsal view, an, anus ; e, hind- 

 gut ; h, hepatic appendages of the 

 mid -gut (all of which are not 

 figured) ; m, mid-gut ; ph, pharynx. 

 (From Lankester, after Alder and 

 Hancock.) 



different groups. Primitively there were two lobes, as in other 

 Molluscs, and this number is, as a rule, retained in- the Gastropods, 

 but there are very few forms in which the lobes are equal and 

 symmetrical, as in Neritina and Fakata. More frequently the topo- 

 graphically left lobe is more deeply involved in the spire, and is 

 larger from larval life onwards than the right lobe in dextral Gas- 

 tropods (Figs. 61 and 116, B) ; the reverse is the case in sinistral 

 forms. The right lobe may disappear, and the left lobe only persist 



