THE ANALYSIS OF NEUROMUSCULAR MECHANISMS IN 



CHITON. 



By W. J. CROZIER. 

 (From the Hull Zoological Laboratory, University of Chicago, Chicago.) 



(Received for publication, May 3, 1920.) 



From the standpoint of its grosser structure the nervous system of 

 Placophorans is but poorly centralized, as evidenced by the absence 

 of clearly defined ganglionic concentrations upon its principal strands. 

 Histologically, the character of this nervous system is incompletely 

 known. From the functional side, evidence has been secured point- 

 ing to the relatively diffuse type of nervous organization prevailing 

 in Chiton as compared with some other moUusks (Arey and Crozier, 

 1919). It was desirable to make further inquiry as to the nature of 

 the nervous organization of Chitons, especially as revealed through 

 the actions of alkaloids. The species employed was Chaetopleura 

 apiculaia Carp, (found at Woods Hole, Massachusetts). 



The neuromuscular responses of Chitons comprise movements of 

 various parts of the body, resulting from localized stimulations, and 

 movements of the animal as a whole. In the latter category are 

 included locomotion, suctional attachment to a substratum, and 

 curling up movements. 



The locomotion of Chaetopleura, like that of other Chitons {cf. 

 Crozier, 1918-19), is accomplished by neuromuscular waves which 

 travel from anterior end to posterior end over the surface of the foot. 

 In this species, as in other cases, one pedal wave at a time usually 

 appears on the foot, although in the larger specimens (20 mm. in 

 length and over), two or three successive waves may be seen on the 

 foot simultaneously. 



Chaetopleura is negatively photo tropic when exposed to light of 

 150 or more meter candles intensity; to Hght of less than 150 meter 

 candles the older individuals are indifferent. An animal creeping in 

 bright light ceases movement when the light is removed, but the shell 

 surface is not sensitive to a decrease of light intensity. 



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