632 NEUROMUSCULAR MECHANISMS IN CHITON 



Nicotine. 



Attached Chaetopleura immersed in 1:25,000 solutions of nicotine 

 (Kahlbaum) within 3 minutes release their suctional attachment 

 to a surface, and curl ventralward rather sharply at both extremities. 

 The proboscis fold is commonly much protruded, covering the an- 

 terior end of the foot. The girdle is curled inward. In this tightly 

 curled condition the Chiton quickly passes into paralysis. After 15 

 minutes in nicotine solution, recovery of normal movements is effected 

 within an hour following return to sea water. At 1:1,000 concen- 

 tration the nicotine effect is almost instantaneous. After the first 

 few seconds in nicotine solution the ordinary responses to changes in 

 illumination are obliterated. 



Nicotine primarily induces the contraction of flexor muscle groups 

 (ventral girdle muscles, lateral shell muscles), whereas in the early 

 stages of strychninization the extensor antagonists of these muscles 

 are the most readily contracted. 



A further peculiarity of the nicotine action consists in its selective 

 nature. The anterior end of the Chiton is almost invariably more 

 strongly flexed than the posterior. When curled up in the absence 

 of nicotine, the posterior end is the more flexed, the anterior end 

 folding over it. When the body has been partially transected in such 

 fashion that the soft tissue of the foot is separated from the proboscis 

 fold, while the dorsal muscle bands are left in continuity, it is found 

 that nicotine induces as promptly as before the general flexion of the 

 girdle, while the foot and shell muscles remain for a long time un- 

 affected. The action of strychnine on such a preparation, already 

 noted, is quite different. Thus the "cerebral" region of the nervous 

 system of Chiton, despite the absence of pronounced cephalization, 

 exhibits nevertheless a certain degree of selective reactivity with 

 nicotine, homologous with that demonstrated by Moore (1918-19) 

 for the cerebral ganglia of the squid. 



Curare. 



Immersion of a Chiton for 3 hours in a saturated emulsion of 

 active curare has practically no detectable results on the animal's 

 movements. Detached and partially curled up Chaetopleura dropped 



