GASTEROPODA. Ard 
and the stomach a simple membranous sac; whilst in olis 
the liver is disintegrated, and its canals so large that the 
process of digestion must be chiefly carried on in them, and 
they are regarded as ccecal prolongations of the stomach; the 
coeca extend into a series of gill-like processes, arranged upon 
HN i 
Fig. 189. Dendronotus arborescens. 
the back of the animal, which also contain part or the whole of 
_the true liver; the gastric ramifications vary exceedingly in 
amount of complexity. The Doridide are distinguished by 
haying a short and wide lingual membrane with numerous 
similar teeth ; the AXolids have a narrow ribbon with a single 
series of larger teeth. In Dendronotus a large central tooth is 
flanked by a few small denticulated teeth. (Alder and Hancock, 
Ei i. Hic. 8.) 
The only Nudibranch with a solid upper jaw, is Zgirus 
punctilucens (A. and H., Pl. XVII., Fig. 15). In other instances 
the two halves are articulated and act as lateral jaws. In 
4fgirus the mouth is also furnished with membranous fringes 
(A. and H., Pl. XVIL., Fig. 14). Ancula cristata has a for- 
midable spinous collar (Pl. XVII., Fig. 7). 
(ye AY 
Ny ¥ 
‘ } 
Bg 
a 
77) 4 
6, Horny upper mandible detached. 
c, Prehensile collar of Ancula. 
a, mantle ; 2, dental sac; 0, insertion-plate of mandible ; c, passage of mouth. 
The yascular system and circulation of the nudibranchiate 
molluses is incomplete. In Doris veins can be traced only in 
the liver and skin; the greater part of the blood from the 
arteries escapes into the visceral sinus and into a network of 
