94 



THE GASTROPODA 



and extensive cuticle, which is generally more fully developed near 

 the origin of the intestine, and may extend into it, as in Paludina, 

 Cydostoma, and certain Pulmonates. Sometimes this lining presents 

 a specialisation in the form of a longer or shorter cuticular projec- 

 tion known as the crystalline style, which may be lodged in a thick- 

 walled caecum or may project as a rod into the proximal part of 



Pio. 75. 



Pteroceras, right-side view of the male, with the mantle laid open, a, anus ; b.d, bile-duct ; 

 c.g, cerebral ganglion ; cr.s, crystalline style ; /, foot ; g, gill ; g.fi, gonad ; g.o, genital orifice ; h, 

 heart ; hy.g, hypobrancliial gland ; i.g, infra-intestinal gland ; in, intestine ; k, kidney ; m, 

 mouth ; oe, oesophagus ; op, operculuin ; p, penis ; pa, mantle ; p.g, pedal ganglion ; pl.g, plural 

 ganglion ; ra, radula ; r.o, renal orifice ; r.p, reno-pericardial orifice ; s.g, supra-intestinal gan- 

 glion ; *i, siphon ; s.gr, seminal groove ; st, stomach ; t, tentacle. (After F. M. Woodward.) 



the intestine. This structure is found in various Docoglossa, 

 temporarily at least in Fissurella, in Trochus, in numerous Hydro- 

 biidae such as Bithynia, Lithoglyphus, Spekeia, Tanganyicia (Fig. 78, cr.s), 

 etc., in the Melaniidae and allied forms such as Paramelania, Nas- 

 sopsis, Typhlobia, etc., and in Pteroceras (Fig. 75, cr.s} among thp St.rom- 

 bidae. In many cases the stomach is furnished with a caecum, 

 generally pyloric in position and contiguous to the openings of the 

 hepatic ducts. This caecum is coiled in a spiral in many Rhipido- 



