24 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
While all of the inhabited valleys support the same kind of flora, whose ele- 
ments are arranged in the same zonal manner, yet the relative abundance of the 
several representatives varies strikingly. One may contain an abundance of cala- 
dium and plantains, such as Fautaua, while a neighbor like Tipaerui will have a far 
greater proportion of turmeric, ginger, and Dracena; yet it is impossible to discover 
any correlation between the dominance of a nurse-plant and the characters dis- 
played by the snails of a given valley; in valleys with the same prevalent type of 
plant the snails may be identical or dissimilar, while in valleys that display different 
botanical conditions the snails may also be the same or unlike one another. 
Passing now to the general zoological conditions, the most striking feature is 
the paucity of animal life in the valleys, aside from insects and the snails themselves. 
No invertebrates have been found to be enemies of the Partule, although there may 
be minute or microscopic species that are parasitic upon them. Lizards are abun- 
dant everywhere, but usually insectivorous, and would scarcely prey upon a snail 
provided with a large, thick shell. Birds are surprisingly few in species and in numbers 
and they are either small insectivorous forms or larger fruit-eating species. The 
introduced rat is the only animal that may directly concern the Partulz in a slight 
degree. In the lower areas of the large valleys shells have been found that had 
certainly been gnawed by rats; they belonged to all of the species and color varieties 
that existed in such valleys. The snails remain during the day on smaller shrubs 
and plants upon which rats can not climb, and as the latter are not abundant save 
in the neighborhood of the coast, where Partule are few in numbers, we would 
scarcely regard these mammals as having an important influence upon the charac- 
teristics or even the abundance of land-snails of any species. 
THE HABITS AND SPECIAL NATURAL HISTORY OF PARTULZ. 
Hitherto we have been concerned with the environmental conditions that 
affect the distribution of Partule by limiting their sphere of habitation to restricted 
valley areas in islands like Tahiti. We may now turn to the special consideration 
of the habits of the snails and of their reactions to external energies, as these are 
observed within the inhabited regions. Besides the observations upon the animals 
in the field, much has been ascertained through the study of snails in captivity in 
the laboratory, as regards the relation of Partule to gravity, heat, moisture, and light. 
Three groups of species can be distinguished on the basis of reactions to gravity. 
P. producta in Tahiti is a type of the forms that live always on the ground, lurking 
under stones, dead trees, and dead leaves, such as those of the caladium and plan- 
tain. Ina species like P. fusca of Raiatea the animals are not always confined to 
the ground, but will climb upwards to a height of 3 or 4 feet to rest under the leaf- 
sheaths of a plantain, or more infrequently on the external surface of a trunk itself. 
The second group comprises the greater number of species in Tahiti, in the Society 
Islands and elsewhere, whose representatives are arboreal during the daytime, 
remaining sealed up on the under sides of leaves less than 10 to 15 feet from the 
ground; at night, however, they resume activity and crawl to the earth to feed upon 
