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LESLIE B. AREY AND W. J. CROZIER 



corresponds with that of some other chitons (Heath, '99, '05 b 

 '05 c), at least for the early years. It is also true that in certain 

 other chitons the second year marks the incidence of sexual 

 maturity (Heath, '05 c) . The large Cryptochiton stelleri grows 

 more rapidly than Chiton tuberculatus does, but also matures in 

 the second year (Heath, '05 c). 



The curve in figure 5 is introduced here for the purpose of 

 correlating some statements to be made subsequently regarding 

 behavior at different ages (cf. Crozier, '18 b). 



1 a 3 4 5 6 7 8 9 Yrs. 



Aq e, estirr? afed . 



Fig. 6 The frequency distribution of estimated ages in the chiton popula- 

 tion on the north shore of Long Island, Great Sound (April, 1918). It is neces- 

 sary to consider each local population separately. The one here plotted is fairly 

 representative. 



3. Destructive agents 



The power with which chitons may adhere to the rock surface 

 is well known. When disturbed the girdle is firmly applied to 

 the surface and the shell plates closely approximated. Except 

 by means of a very powerful lateral push, it is impossible to dis- 

 lodge them, once they are 'set' (which may happen very quickly) ; 

 there is no projecting part of the smooth depressed animal which 

 could offer a 'hold. ' The dead plates found in the field have almost 

 without exception been those of animals eight to nine years old. 



