NATURAL SELECTION NOT ALWAYS THE CAUSE. 219 
which are genera of terrestrial habits, are (with but few exceptions) 
dextral in form; while the other genera, which are plant feeders and 
constantly hanging to branches or leaves, present many species that are 
‘ constantly sinistral, and many others that are both dextral and sinis- 
tral. Why should Achatinella adustain Pauoa and Makiki be constantly 
sinistral when the most nearly allied A. producta found in the same 
valleys is both dextral and sinistral? Why should A. bacca and A. 
abbreviata in Palolo and Waialae be constantly dextral when other 
species of Achatinella in the same valleys are for the most part sinistral ? 
Is there any adaptation to the environment possessed by a dextral 
form which would be lost if the form was reversed? If not, natural 
selection could not have anything to do with that part of its char- 
acter. Bulimella rosea is sinistral, while B. bulimoidesisdextral. If 
in this respect they should exchange forms, would any disadvantage 
be experienced by either species? It is impossible to conceive of any 
disadvantage that would follow, and, therefore, I can not believe that 
this difference in the two species was in the first place due to natural, 
sexual, or any other form of selection. 
There are many other specific distinctions presented in this family 
which seem to be of no advantage, though they are not so far removed 
from all suggestion of the possibility of use as the character we have 
just been considering. The brilliant colors and varied patterns pre- 
sented by many of the arboreal species would be of advantage to them- 
selves if they served as warning of nauseous qualities to creatures that 
are liable to prey upon them; but no such conditionsexist. The birds 
of the forest region are for the most part fruit and nectar feeding; 
and the ants and mice which in recent years have made sad havoc 
with the mountain snails unfortunately do not spare the highly colored 
species. 
There can be no doubt that when representatives of different genera 
occupy the same trees they remain segregated through the influence 
of sexual instincts, which must be associated with some means of rec- 
ognizing those of their own group; but it is not at all probable that 
the colors and patterns of any species are recognized by their mates, 
or have been developed under the influence of sexual selection. 
There is, therefore, strong reason to doubt whether selection of any 
kind has been concerned in the production of the beautiful colors and 
patterns of these species, unless possibly correspondences in color 
within the limits of a genus are, in some cases, due to the inheritance 
of tendencies produced by selection when conditions were very differ- 
ent from what we now find. But the divergences in color and pattern 
in the species of one genus can not be thus explained. 
