ZOOLOGY: W. J. CROZIER 
325 
The mean duration of life is probably a little less than eight years. This 
curve affords a basis for comparing the growth of chitons in differing 
environments. 
1 Contributions from the Bermuda Biological Station for Research, No. 96. 
2 Cf. Crozier, W. J., Amer. Nat., New York, (in press), and Arey, L. B., and Crozier, W. J., 
(in press), for an account of observations forming the starting point of these investigations. 
3 Winge, 0., Medd. Komm. Havunders., Fisk., Kobenhavn, 4, No. 8, 1915. 
4 Heath, H., Zool. Anz., Leipzig, 29, 1905, (390-393). 
GROWTH OF CHITON TUBERCULATUS IN DIFFERENT 
ENVIRONMENTS 1 
By W. J. Crozier 
Bermuda Biological Station for Research, Dyer Island, Bermuda 
Communicated by E. L. Mark, September 30, 1918 
In the preceding paper a mean growth-curve for the chiton population of 
Great Sound, Bermuda, was derived from the examination of 1090 individuals, 
on the assumption, supported by collateral evidence, that the age of a chiton 
may be estimated from the markings upon its shell-plates. It was pointed 
out that curves of this kind might be used to study variations in the growth 
of Chiton tuberculatus in differing environments. A test of this suggestion 
is afforded by the comparison of the rates of growth and of the average dura- 
tion of life of this species when living (1) in Great Sound, (2) on the south 
shore of Bermuda. 
Even within the limits of Great Sound itself the chitons inhabiting the shores 
of the several islands may exhibit differing rates of growth, as indicated in 
figure 1. When two such islands as Long Island and Grace's Island are com- 
pared, it is found that the chitons from the former place grow somewhat less 
rapidly than do those from the latter, although the initial growth-rates are 
identical. Most of the Long Island chitons occur on the north shore of that 
island, which is a cliffed shore with many caves, sheltered from the sun but 
exposed to the beating of the sea during northwest winter gales. Grace's 
Island is more sheltered from storms. 
On the other hand, chitons from an exposed beach on the south shore of 
Bermuda, such as that at Cross Bay, which supports a more numerous chiton 
population than do situations within the stiller waters of the Sound, grow at 
first more rapidly, but after the first year are smaller, as compared with those 
living in Great Sound. 
The physical differences between two such environments as those presented 
by Long Island and by the beach at Cross Bay, include at least the following: 
the sea-water on the south shore is more alkaline, contains more oxygen, and 
is lower in temperature; the algal food for the chitons is not only specifically 
