SELECTION NOT ALWAYS THE CAUSE. 5 
that they possess the power of discriminating colors, we must seek 
some other explanation. If the colors were of a protective character 
we might surmise that they had been developed through exposure 
for many generations to sharp-sighted enemies; but in the case of 
many of the species, their white and green tints striped with black 
make them conspicuous objects against the brown trunks of the trees 
on which they are constantly found. Neither are their colors for 
warning; for these snails are not repulsive to flesh-eating birds. It 
is, therefore, hard to avoid the thought that these striking colors are 
of no service in protecting the life, either of the individual or of the 
species. Again, certain birds of prey are the only aboriginal crea- 
tures that could be suspected of feeding on these snails; and as the 
birds have a wide range, the immense diversity of color in the snail 
shells of one island would remain unexplained. 
There is, also, another character in which species of some of these 
genera often differ from each other, in regard to which natural selec- 
tion has never been shown to be the controlling factor. I refer to the 
character of the coil of the shell, which may be dextral in one species, 
sinistral in another, and either dextral or sinistralin a third. As long 
as it is impossible to give any reason why a species would not be 
equally successful if every individual possessed the reverse form from 
that it now has, it is unreasonable that we should attribute the pres- 
ent form to the influence of natural selection. 
The theory that there is great advantage for the species in having 
all the individuals coiled in the same way, if proved, would in no way 
explain why certain species are always dextral and certain others are ~ 
always sinistral, while some well-established species present large 
masses of individuals of each form. I think it will some day be 
shown that snails of opposite forms, though of the same race, are in- 
capable of mating with each other, and we already know that each 
individual is both maleandfemale. If, then, an unusual sport should 
produce, in the same family, or on the same tree, two individuals of 
the reverse form from their parents, we should have a completely 
segregated variety established in the original home, while exposed to 
the same environment and using it in the same way, and its new char- 
acter conferring no benefit. 
Third. Because in the case of certain divergent species of Achatinella, 
occupying tsolated valleys presenting the same vegetation, the diversity of 
selection to which they are subjected through different habits of feeding is 
directly preserved by the rsolation which prevents the peculiar habits from 
being broken down by free crossing. The habits of feeding are not with- 
out variation even in the original valley. When, therefore, one or two 
