NERVOUS SYSTEM OF INVERTEBRATES. 



91 



still simpler, since it lacks the locomotive ganglion 

 (Fig. 64). 



2. In gastropods, as the snails (Fig. 65), we find, 

 (1) as usual, the cephalic ganglia and oesophageal col- 

 lar in which are lodged all the higher functions— con- 

 sciousness and volition, control of 

 voluntary movements, etc. ; (2) in 

 the foot or crawling disk a gan- 

 glion to preside over locomotion ; 

 (3) visceral ganglia in the visceral 

 region, appropriately placed. All 

 are, of course, connected with the 

 cephalic ganglion and dominated 

 by it. In the figure, however, only 

 the oesophageal collar is repre- 

 sented. 



3. In cephalopods (squids, cut- 

 tlefish, etc.) (Fig. 66) we have (1) 

 a large ganglion in the head com- 

 pletely and closely encircling the 

 gullet, and forming a very per- 

 fect close-fitting oesophageal col- 

 lar. This is doubtless a combina- 

 tion of cephalic and oesophageal 

 ganglia. It controls the move- 

 ments of the jaws and arms, and 

 it presides over the higher senses of sight and hear- 

 ing, which are well developed in these animals. It is 

 the seat of conscious voluntary motion and of what- 

 ever higher faculties the creature may possess. (2) Be- 

 sides this there are a pair of locomotive ganglia in the 

 muscular mantle to control its contraction. (3) A large 

 visceral ganglion presiding over nutrition and respira- 

 tion. All of these are, of course, connected with the 

 head ganglion. 



Fig. 65. — Nervous system 

 of a gastropod : c, ce- 

 phalic ganglion ; e, oeso- 

 phageal ganglion. 



