THE AMPH1NEURA 



49 



The two great ventral or pedal cords give rise to the pedal 

 nerves. The two great lateral or pallial cords chiefly send nerves 

 to the mantle and the gills, and thus correspond to the whole of the 



pleural ganglia and the pallial 

 ^^ nerves of the other Mollusca; 



a great part of the viscera 

 (genital glands, kidneys, and 

 heart) also receives nerves from 

 these pallial cords. 



The little differentiated 

 head region bears no special 

 sense-organ, except that the 

 outer edges of the snout taper 

 to form the labial palps. The 

 lower wall of the buccal cavity 

 is furnished with cyathiform 



gustatory bodies, whose nerves 

 arise from the cerebral commis- 



xn 



XI 



Fio. 81. 



Nervous system of Acanthochiton dis- 

 crejxins, dorsal aspect. I, upper buccal 

 commissure ; II, upper buccal ganglion ; 

 III, stomato-gastric commissure ; IV, labial 

 commissure ; V, subradular ganglia and com- 

 missure ; VI, anterior (larger) pedal commis- 

 sure ; VII, peflal cord, with pallio - pedal 

 anastomoses ; VIII, supra-rectal pallial com- 

 missure ; IX, pallial cord; X, pedal anas- 

 tomosis; XI, stomato-gastric ganglia and 

 radular nerves; XII, oesophageal nerves; 

 XIII, cerebral commissure. 



Placiph&rdla stimpsoni, ventral aspect ; 

 nearly natural size, a, anus ; ci, pallial 

 cirrhi ; g, gills (between the two rows of 

 gills is the oblong foot) ; w, mouth ; jm, 

 mantle ; te } tentacles of the interior edge 

 of the mantle. (After Plate.) 



sure ; and, in front of the radula, there is the above-named " sub- 

 radular organ," an epithelial projection, with nervous endings, lying 

 on the two small subradular ganglia, and probably gustatory in 

 function (Fig. 31, V). 



4 



