n6 



THE GASTROPODA 



especially in the Pulmonata, in which group the pleural ganglia 

 scarcely ever give off any nerves. In all the Euthyneura except 

 Adaeon (Fig. 57), Chilina, and Latia (Fig. 96) the infra-intestinal 

 ganglion is fused with the abdominal (Fig. 97, ab) in such a manner 

 that the latter appears to participate in the innervation of the 

 mantle for instance, in the innervation of the inferior pallial lobe 

 and the pallial branchia of the Planorbidae and the pallial nerves 

 issuing from the left moiety of the visceral commissure originate 

 from a special and newly -developed ganglion, viz. the parietal 

 ganglion of the Pulmonata (Figs. 96, g.pa' } 97, sp). As regards the 

 viscera, the heart, the kidneys, and the gonad receive their essential 

 nerve supply from the abdominal ganglion, the alimentary canal 

 receives its nerves from the stomato-gastric centres, and these latter 

 nerves sometimes exhibit accessory ganglia on specialised parts of 

 the alimentary tract, such as the gizzard of Tectibranchia, etc. 



5. Sense Organs. In addition to sensory cells scattered over the 

 whole surface of the body, Gastropods possess special sensory 

 organs usually designated by the names rhinophore, osphradium, 

 otocyst, and eye. While the whole surface of the integument is 

 sensitive, tactile sensibility is more particularly localised in the 

 anterior regions of the body : in the head, in the margin of the 

 foot (in marine Streptoneura the whole ventral surface of the foot 

 exhibits a fine nervous network), and in the regions of the body 

 specialised to form tactile appendages of various shape and situa- 

 tion. Such are the cephalic tentacles especially the anterior pair 

 in quadritentaculate Euthyneura ; the labial palps (Fig. 117, te"\ 

 which bear a row of tubercles in some Pulmonates; the pedal 

 tentacles of Vermctii-s (Fig. 45, p.t) ; the epipodial tentacles of the 



Rhipidoglossa (Fig. 130, XI), 

 which have ciliated sensory 

 organs at their bases; and 

 the pallial appendages, such 

 as the dorsal papillae of the 

 Nudibranchs. 



The Rhinophores, or olfac- 

 tory organs, as they are called, 

 are likewise constituted by 



Bulla (//fimtnea) navicula, ri^ht-side view, c.h, the Cephalic tentacles, CSpeci- 

 cephalic hood; , eye; /, foot; h.o, hermaphrodite ,, , r Al . . r . 



oritice; i.1, inferior pallial lobe; m, mouth; m.o, ally by the posterior pair 111 



male orifice ; r/i, rhinophore (Hancock's organ); s.g, .1 miadritpntannlutp Fiithv 



seminal groove ; sh, shell. (After Guiart.) tne quaanteniaCUldl/e J!Altny- 



neura. The whole surface of 



these tentacles is covered by little ciliated papillae, giving them a 

 silky appearance, in many Rhipidoglossa, e.g. Scissurella, Haliotis, 

 Trodius, Gena, Molleria, Cyclostrema, Neritina, in Caecum (Fig. 68, te), 

 etc. The olfactory nerve divides into many ramifications which end 

 on the surface of the tentacle in olfactory sensorial cells. In many 



Fid. !)8. 



