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LESLIE B. AREY AND W. J. CROZIER 



erence more specifically to some definite peculiarity of behavior. 

 These tests were made with chitons of relatively large size (6 to 

 8 cm.) in which the shell valves were probably more or less eroded, 

 although at the time no special note was made of their condition. 

 /3. Analyses of responses to general illumination. The fore- 

 going section indicates the somewhat obscure relations, with 

 respect to phototropism, discovered in random samples of the 

 chiton population. The younger individuals, especially those 

 less than 2 cm. long, live in dark situations. When stones 

 bearing them are turned over, the chitons creep rapidly to the 

 under, dark side. Not until a length of 7 to 9 cm. is attained 

 does Chiton occur with any frequency upon illuminated rocks. 

 If chitons from habitats representing these two divergent ex- 

 tremes are compared, it is found that in ordinary sunlight the 

 larger ones are photopositive, the younger ones photonegative. 

 Their orientation is precise, definite, and without ^ trial move- 

 ments.' There are, however, certain complications in the mode 

 of orientation which will be fully considered on a later page. 

 The fohowing test is typical:^ 



^ The specific animals bear definite numbers given to them in the field note- 

 book. In a subsequent report on the ethology of C. tuberculatus the necessity 

 for this will be made apparent. 



