160 THE AMERICAN NATURALIST. (VOL. XXXIII. 
clusions are that the “white children present more diversity, negro 
children more uniformity, in all their normal physical characters.” 
The American Antiquarian for the year 1899 will contain a list of 
accessions to, and of the specimens available for exchange in, the 
anthropological museums of America. This novel feature com- 
mends itself to the attention of curators. The appearance of Anti- 
guarian would be greatly improved by more careful proof reading. 
FRANK RUSSELL, 
ZOOLOGY. 
Dimorphism in Crepidula. — An interesting instance of environ- 
mental and sexual dimorphism is described by Prof. E. G. Conk- 
lin? in the sedentary gasteropod Crepidula. In C. convexa there 
are marked local varieties depending upon the immediate environ- 
ment; for example, when found upon the shells of Illyonassa or 
Littorina it is deeply convex and darkly pigmented, but on oyster 
shells it is very much flatter and lighter in color. Also among the 
larger species, C. fornicata and plana, marked differences in the form 
of the shell occur, which are due to the nature of the substratum — 
to which they are attached. These irregularities in form are not 
inherited and are cited as examples of “environmental poly- 
morphism.” Dimorphism in Crepidula plana is exhibited by the 
occurrence of a dwarf form in addition to the normal one. The 
latter is found inside of dead shells of Neverita inhabited by the 
large hermit crab Aupagurus bernhardus, while the dwarf is found in 
the smaller shells of Illyonassa and Littorina, inhabited by the little 
hermit Zupagurus longicarpus. ‘The disproportion between the nor- 
mal and dwarf forms is considerable, the former being about thirteen 
times as large as the latter, as was determined by measurement of 
body volumes. Age and sexual maturity are attained in the dwarf 
as in the normal type. All of the organs of the body are reduced in 
size in about the same proportion, but the cell size in homologous 
organs of the two forms, including the ova and embryos, is constant. 
There is thus a smaller number of cells present in the various organs 
and also in the entire body of the dwarf than in the giant. The 
dwarfed form is correlated with the small size of the shell in which 
1 Conklin, E.G. Environmental and Sexual Dimorphism in game Proc. 
Acad. Nat. Sci., Philadelphia (1898), pp. 435-444, Pls. XXI-XXII 
