630 NEUROMUSCULAR MECHANISMS IN CHITON 



plates results in the approximation of these two plates, thus covering 

 the spot irritated; this reaction is in no way modified under strych- 

 nine (even at 1:4,000 concentration). The girdle, also, responds in 

 an entirely normal fashion to local tactile activations, as do the 

 ctenidia. Another form of response which remains unaltered under 

 strychnine is the dorsalward contraction of the ctenidia against the 

 roof of the ctenidial channel when a spot on the same side of the foot 

 is touched. The surface of the foot itself exhibits an interesting 

 modification of its responses; the foot ordinarily responds to the 

 contact of a surface, sufficiently large with respect to the foot, by a 

 positive suctional attachment (the adhesion of the foot being due to 

 the activity of many minute suctional fields over its surface); but 

 under strychnine, the foot puckers away from the contact of a surface 

 of any size — its positive stereotropism suffers reversal. In the non- 

 strychninized Chiton the touch of a fine-pointed rod causes merely a 

 localized but rather deep puckering of the foot. Under strychnine, 

 touching one small point leads to a widespread retraction. 



With more concentrated solutions (1:4,000) these effects develop 

 more promptly. The body becomes at first greatly arched, the 

 back convex, with some convulsive trembling, but the girdle does not 

 curl ventrally. If touched on the back, the animal usually ceases to 

 adhere to the bottom and curls up, armadillo fashion, remaining so 

 for some minutes. Ultimately, even in strychnine of low concen- 

 tration (1:12,000), the Chitons pass into a paralyzed state, with all 

 muscles contracted, the girdle curled ventralward, the two ends of 

 the body more or less approximated ventrally. 



The significant features of these results are: (1) The reversal by 

 strychnine of the suctional attachment of the ioot;^ (2) the neuro- 

 muscular reversals exhibited in the dorsalward curvature of the 

 girdle and of the body as a whole, probably due to the effects of im- 

 pulses originating in those parts at the time in contact with the sub- 

 stratum; (3) the reversal of the response to increased illumination of 

 the ventral surface; (4) the fact that certain responses seem to remain 



^ This is paralleled by Moore's (1916-17) finding with the tube feet of strych- 

 ninized starfish. 



