HEAD AND ITS APPENDAGES. 



11 



remarkable disturbance. The visceral sac may, however, have a 

 flattened or cylindrical form and retain its symmetry. In this 

 group (the Cephalophora) the shell may be simply plate-shaped or 

 spirally wound, or remain as a mere flat rudiment hidden under the 

 dorsal integument. In one group of the Cephalophora, viz., the 

 Cephalopoda, a circle of arms is attached to the head around the 

 mouth opening. They serve both for swimming and creeping, and 

 for the capture of nourishment. By Loven and K. Leuckart they 

 were looked upon as modifications of the buccal lobes ; by others, 

 perhaps with greater justice, as tentacles, and by others again as 



Oc Te 



JBii 



FIG. 494. Male of Carinariamtdlterranea (after Gegenbaur). P, Foot ; S, sucker; 0, mouth ; 

 m, buccal mass ; M, stomach ; Sp, salivary gland ; L, liver ; A, anus ; CG, cerebral 

 ganglion; Te, tentacle ; Oc, eye; Ot, auditory vesicle; EG, buccal ganglion ; Pg, pedal 

 ganglion; Mg, mantle ganglion; N, kidney; Br, gill; At, auricle; Ve, ventricle; Ar, 

 aorta ; Z, hinder branch of the same ; T, testis ; Vd, vas deferens ; Wp, ciliated furrow ; 

 Pe, penis ; F, flagellum with gland. 



modifications of the foot. A perforated funnel-shaped cone, through 

 which the excretory products and water which has passed over the 

 gills is expelled from the large mantle cavity, and which thus 

 serves at the same time as a swimming organ, probably corresponds 

 to the fused folds of the epipodia. Amongst the Gastropoda the 

 head is provided with tentacles and buccal lobes, and the ventrally 

 placed foot possesses a large flat plantar surface ; more rarely it has 

 the form of a vertically placed fin (Heteropoda, fig. 494). In another 

 group, the Lamellibranchiata (Acephala), there is no independent 

 head, and the laterally compressed body bears two large lateral mantle 



