454 PROCEEDINGS OF THE ACADEMY OF [June, 



(1) The curve of growth, fig. 2, shows that those in the surf 

 environment at a given age are smaller than those from the bay- 

 environment. 



(2) There is a tendency toward dark individuals. 



(3) There is a tendency toward lamellated forms. 



These studies show that natural selection has some determining 

 action on the color varieties present. (1) It has been shown that 

 the color of the rocks, whether dark or light, has an effect. (2) It 

 has been shown that the white barnacle-covered rocks contain more 

 light-colored ones than those on the mussel bed but a few feet away. 

 (3) It has been pointed out that those living on rocks near mud 

 flats are darker than on the more exposed points of the same islands. 



The present study must leave the question of the relation of the 

 yellow forms and the striped forms to the color of their substratum 

 yet unsettled. 



In general, however, there is a relation between the color and the 

 environment. This relation is caused by natural selection and not 

 by the direct action of the environment. 



List of Literature. 



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Nat, Sci., XIV, pp. 131-137. 

 Blaney, D. 1904. Proc. Boston Soc. Nat. Hist., Vol. XXXII, No. 2. 

 Carpenter, W. 1857. On the Development of Purpura. An Mag. Nat, 



Hist,, 2d Series, Vol. XX. 

 Cooke, A. H. 1895. Cambridge Natural History, Vol. Ill, The Mollusks, 



pp. 69, 90. 

 Cooke, A. H. 1915. Proc. Mai. Soc. London, p. 193. 

 Glaser, O. C 1905. Ueber den Kannibalismus bei Fasciolaria tulipa (var. 



distans), Zeit f. wiss. Zool., Bd. LXXX, p. 80. 

 Gould, A., and Binney, W. G. 1869. Invertebrates of Massachusetts, 2d Ed., 



Boston, pp. 360-362. 

 King, L. A. L., and Russell, E. S. 1909. A Method for the Study of the 



Animal Ecology of the Shore. Proc. Rov. Phvs. Soc. of Ed., Vol. XVII, 



pp. 225-253. 

 Pelseneer, P. 1904. Le Mode de Nutrition des Embrvons de Purpura lapillus. 



Cong. Zool., VI, pp. 343-345. 

 Robert, A. 1902. Recherches sur le developpement des Troques. Arch. 



Zool. Exp., 3 ser., X, No. 3. 

 Shelford, V. 1913. Animal Communities in Temperate America. Univ. oi 



Chicago Press. 

 Sumner, F. B., Osburn, R, C, and Cole, L. J. 1911. A Biological Survey ol 



the Waters of Woods Hole and Vicinity. Bull, of the Bureau of Fisheries, 



Vol. XXXI. 

 Walter. 1910. Variations in Urosalpinx. Am. Nat., Vol. XLD , No. o26 r 



October. 



