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ZOOLOGY: W. J. CROZIER 
GROWTH AND DURATION OF LIFE OF CHITON T UBERC ULA T US 1 
By W. J. Crozier 
Bermuda Biological Station for Research, Dyer Island, Bermuda 
Communicated by E. L. Mark, September 30, 1918 
The common chiton of the Bermuda Islands, C. tuberculatus L., passes all 
of its post-larval and adult life within the limits of the tidal zone. A thor- 
oughly representative sample of the total chiton population is therefore ob- 
tainable, though with difficulty in some places. In certain specific locations 
it has been possible to study practically all of the chitons there existing. In- 
dividuals are of various sizes, ranging during the spring months from 0.6 to 
10 cm. in length. The frequency distribution of the lengths of the chitons at 
each locality is of an obviously multimodal character. It seemed likely, then, 
that one could work out some of the main features of the growth and duration 
of life of this mollusk. Facts of this sort, of which in the natural history of 
marine invertebrates there is a conspicuous deficiency, are not only important 
in a purely biological way, but have also a bearing upon the problem of esti- 
mating in outline the general fertility of the sea. This paper embodies a pre- 
liminary report upon one phase of an investigation having to do with the eth- 
ology of the chitons, especially from the standpoint of analyzing their behavior 
under natural conditions. 2 In a subsequent paper it will be shown that the 
growth phenomena in chiton probably afford a basis for the consideration of 
important questions which it has been impossible to approach successfully in 
such growth-studies as have previously been made on some other organisms 
in the warmer seas (e.g., Madreporarians). In this paper data are summa- 
rized establishing mean growth-curves for chitons inhabiting the region of 
Great Sound, Bermuda; although the chiton environments comprised within 
this region, a semi-enclosed sound, are ethologically far from being of a strictly 
homogeneous type, they nevertheless agree in certain significant physical 
respects, wherein they differ from other classes of situations (e.g., shores washed 
by the ocean surf) where chitons of this species also live. 
Each of the eight plates which make up the 'shell' of chiton is compounded of 
a superficial 'tegmentum,' containing sensory receptors (photoreceptors 2 ), and 
of a more deeply situated 'articulamentum.' The central area of the teg- 
mentum of each plate is marked by a series of more or less distinct transverse 
grooves, or 'growth-lines.' The number of these growth-lines, best counted 
upon the six intermediate plates, is constant upon the different plates of one 
individual. On the assumption that these growth-lines, analogous to the 
concentric markings of the scales and otoliths of teleosts, 3 are formed at the 
rate of one per year, it is possible to estimate the growth-rate of chiton. The 
probable correctness of this assumption is assured, (1) by the inspection, 
throughout the year, of the growth of the young chitons appearing after the 
