THE PULMOGASTEEOPODA. 



XIII. THE PULMOGASTEEOPODA. 



These are the Pulmonate Gasteropoda of Cuvier, or the snails 

 and slugs, which agree with the Branchiog aster opoda in the 

 general characters of their body, mantle, nervous and respira- 

 tory systems, and in possessing an odontophore ; but differ from 

 them, not only in breathing air by means of the thin lining of 

 the pallial chamber, but, as I believe, by the direction of the 

 flexure of their intestine. A careful dissection of a common 

 snail, for example (Fig. 16), will prove that, though the anus is 



Fig. 16. 



Fig. 16. Diagram exhibiting the disposition of the intestine, nervous system, &c., in a 

 common snail (Helix), a, mouth ; b, tooth ; c, odontophore ; d, gullet ; e, its dilata- 

 tion into a sort of crop ; /, stomach ; g, coiled termination of the visceral mass ; the 

 letter is also close to the commencement of the intestine, which will be seen to lie 

 under the oesophagus, and not over it as in the whelk ; A, rectum ; i, anus ; k, renal 

 sac; I, heart; m, lung, or modified pallial chamber; n, its external aperture; o, 

 thick edge of the mantle united with the sides of the body ; p, foot ; r, cerebral, 

 pedal, and parieto-splanchnic ganglia aggregated round the gullet. 



situated in the same way as in the Branchiogasteropoda, on the 

 dorsal or haemal side of the body, the primary bend of the 

 intestine is not to the hgemal, but to the neural side, the 

 eventual termination of the intestine on the hsemal side being 

 the result of a second change in its direction. 



How far this neural flexure of the intestine really prevails 



