W. J. CROZIER 631 



relatively uninfluenced by strychnine (movements of the ctenidia, 

 and of the dorsal plates when the intertegmental mantle is touched) .^ 



In the strychninized Chiton sensory impulses originating on the 

 ventral aspect of proboscis, foot, and girdle may be regarded as 

 causing contraction of extensor (dorsal) muscles of the girdle and of 

 the body {median dorsal longitudinal and oblique dorsal muscles). 

 This effect may be accentuated by touching the back of the Chiton. 

 Such impulses normally lead to the contraction of flexor muscles 

 {ventral muscles of the girdle; lateral longitudinal muscles connecting 

 the shell plates) which results in a closer contact between the Chiton 

 and its substratum. 



Reversal of the response to increased illumination of the ventral 

 surface, involving the muscle groups mentioned, operates in the 

 same manner. This seems to be the first recorded instance of experi- 

 mental reversal of the sense of a response dependent upon "differ- 

 ential sensitivity." 



There is a detectable degree of independence in the movements of 

 strychninized girdle and body. Thus at certain stages a touch on 

 the back may cause the girdle to bend ventrally, while the extensor 

 muscles of the back contract; in other instances the back may be 

 arched, while the girdle bends dorsally. The type of local action 

 here indicated is further illustrated by the behavior of Chitons with 

 the pallial nerve strands cut and with the proboscis region isolated 

 from the foot by a transverse cut. Such preparations do not dift'er 

 noticeably from intact animals in their responses to strychninization. 



2 In a number of instances Chitons returned to sea water after having been in 

 strychnine solution for a number of hours were found to pour out great volumes 

 of sperm, at a certain stage in the progress of recovery. The observation is of 

 interest in connection with the view (Crozier, 1920) that the shedding of sperm 

 by male Chitons, although in normal fertilization preceding the liberation of 

 eggs, is in reality induced as a sensory response to substances emanating from 

 females; in these experiments the proper internal concentration of strychnine for 

 the release of the nervous machinery controling sperm discharge seems to have 

 been estabUshed during the outward diffusion of the drug from the Chiton into 

 sea water. 



