THE GASTROPODA 



97 



gland, and in the Fissurellidae there is a longish glandular caecum 

 in the same position, which opens near the anus and lies alongside 

 the rectum as far as the point where the latter traverses the ven- 

 tricle. As a rule, the anus opens on the right side of the body (on 

 the left side in sinistral forms) and more or less in front. But in 

 those forms in which the coiling of the visceral sac is diminished or 

 lost, this flexure of the digestive canal seems to be effaced and the 

 anus lies at the posterior end of the body. This disposition is rare 



Tanganyicia rujilosa, dorsal view, with the mantle laid open, a, anus ; b.p, brood-pouch ; 

 b.p.o, orifice of brood-pouch ; ce.g, cerebral ganglion ; cr.s, crystalline style ; /, foot ; g, gill ; h, 

 heart ; in, origin of the intestine or pyloric orifice of the stomach ; m, mouth ; od, oviduct ; oe, 

 termination of the oesophagus, or cardiac orilice of the stomach ; o.o, oviducal orifice ; os, 

 osphradiuin ; pa, mantle ; st, stomach ; s.i.g, supra-intestinal ganglion. (After Moore.) 



in the Streptoneura, but may be seen in Cypraea and Pterotrachea. 

 It is, on the contrary, common in the Euthyneura, occurring in 

 Doridium, Euncina, Aplysia (Fig. 154), the Doridomorpha (Fig. 79, 

 VIII), Janus, Alderia, Limapontia, Testacella, the Oncidiidae (Fig. 59), 

 and the Vaginulidae (Fig. 87). 



2. The Circulatory System. The blood is generally a colourless 

 liquid containing amoebocytes. It is red in the genus Planorbis 

 (with the exception of P. albus), in which haemoglobin is diffused 

 in the plasma. The muscles of the buccal mass are impregnated 



7 



