160 LESLIE B. AREY AND W. J, CROZIER 



the other hand, the pecuhar disposition of the nervous system in 

 placophorans may allow us to analyze a few generalized, or 

 fundamental, characteristics of the molluskan nervous system. 

 To this end, some acquaintance with the more obvious features 

 of the natural history of Chiton and a knowledge of the variety 

 of its motor responses are essential preliminaries. 



II. NATURAL HISTORY 

 1. Habitat and appearance 



Numbers of C. tuberculatus may almost always be discovered 

 in any intertidal situation where the substratum is hard and firm, 

 not too greatly exposed to wind and waves, free from muddy silt, 

 the water not too stagnant nor the growth of algae too vigorous. 

 The diversity of local habitats includes: freely exposed faces of 

 ciiffed shores, pockets in shore rocks, crevices, the floors of caves 

 with northern or southern exposures, the under surfaces of 

 boulders and slabs of stone, and the under sides of smaller stones 

 on sheltered, shingly beaches. The individuals obtained from these 

 different habitats are not of uniform appearance. The external 

 aspect of the chitons — as determined by their size, their coloration, 

 and the organisms dwelling upon their dorsal surface — is closely 

 correlated with the conditions under which they are individually 

 found to be living. The meaning of this correlation we are not 

 primarily concerned to analyze in this report ; but since the degree 

 of sensory differentiation which we have discovered in Chiton and 

 the complexity of its behavior seem in some ways to be excep- 

 tionally great, as compared with what is known for some other 

 invertebrates, it is necessary to outline a few of the more im- 

 portant features in its life-history. On certain points the state- 

 ments made are of a preliminary kind, and must for the present 

 remain in dogmatic isolation. Materials for a quantitative 

 analysis of the bionomics of Chiton will be made the subject of a 

 separate report. 



The animals used in our experiments were collected in the 

 region of Great Sound. Within this portion of the Bermuda 

 area, to which the application of the following remarks is to be 



