182 LESLIE B. AREY AND W. J. CROZIER 



analysis are too specific. The real problem is to trace to their 

 sources of origin some of the harmonious correlations — involving 

 habits, coloration, and the like — which specific organisms display. 

 For studies of this kind Chiton tuberculatus affords eminently 

 advantageous material. The analysis of its sensory character- 

 istics, forming the body of this report, is taken therefore as the 

 starting point for a series of quantitative investigations in 

 ethology. 



III. MOVEMENTS AND REACTIONS 



For the analysis of the sensory capacities of Chiton we depend 

 upon its motor reactions under various forms of activation. It is 

 therefore necessary to outline the different modes of response 

 exhibited by these animals. The movements of chitons present, 

 in fact, a certain degree of diversity, somewhat at variance with 

 the traditional epithet 'sluggish,' so frequently applied to them. 

 Slow, as a rule, the movements undoubtedly are, and for that 

 reason particularly favorable for examination, as the responses 

 can be studied with precision. The motor reactions of Chiton 

 comprise movements of local parts of the body, bendings and 

 twistings of the animal as a whole, and pedal locomotion. This 

 classification of movements is largely artificial, but convenient. 

 Each of these classes may be dealt with in further detail. 



1 . Local movements 



Local responses may be obtained from almost every part of 

 Chiton. Since the muscular organs concerned in these move- 

 ments are described in Plate's monograph ('97, '99, '01 a), they 

 will not be considered here. The girdle (fig. 10) reacts locally 

 by puckerings and by bending movements. The individual 

 shell plates may be pushed apart from one another, elevated, 

 depressed, and closely approximated. These local responses are 

 involved also in the general movements of the whole animal. 



The local movements of the ventral parts are less directly in- 

 volved in responses of the animal as a whole. At the anterior 

 end (fig. 11), the mouth, a transverse slit, is situated upon a 



