EXPERIMENTS ON MOLLUSKS 



129 



quantity of the spontaneous progressive movements. 

 Destruction of the pedal ganglion, on the other hand, 

 puts an end to all locomotion. Steiner concludes, 

 therefore, that " the 

 pedal ganglion alone 

 has control of the entire 

 locomotion of the ani- 

 nial." This anthropo- 

 morphic conclusion 

 goes too far. The only 

 conclusion we are justi- 

 fied in drawing from 

 this observation is, that 

 the protoplasmic con- 

 necting fibres between 

 the skin and the foot- 

 muscle of the animal 

 pass through the gan- 

 glion. Steiner further attempted to see if he could 

 produce circus-motions by means of a one-sided divi- 

 sion of the oesophageal commissure in other Mollusks, 

 Pleurobranchia and Aplysia. He succeeded no better 

 than in Pterotrachea. One-sidecl destruction of the 

 pedal ganglion in Cymbulia, however, caused paralysis 

 of one-half of the locomotor or^an. The animal 



o 



naturally moved in a circle, for only one wing served 

 as an oar. 



The Cephalopods have an extremely complicated 

 brain (Fig. 34). It consists of a dorsal and a ventral 

 mass, each of which is composed of several ganglia. 



FIG. 34. BRAIN OF SEPIA. 



Cg; cerebral ganglion ; S/>g, supraoesophageal 

 ganglion ; Bg; buccal ganglion ; Tg; ganglia 

 of the tentacles. (After Claus.) 



