GENERAL FEATURES OF POLYNESIAN REALM IN RELATION TO DISTRIBUTION. 25 
decaying vegetation. The third group is typified by P. attenuata of Tahiti and 
Raiatea; the snails of that species remain high up on the leaves of trees, where 
apparently they obtain their food from the twigs, branches, and limbs. This third 
group is characterized by relatively thin, translucent, horny shells, quite different 
from the heavier calcareous structures formed by the ground and arboreal types. 
In brief, the snails of the first group are positively geotactic almost without varia- 
tion, those of the second are positively geotactic at night and negative in their 
reaction during the day, while the species of the third group are negatively geo- 
tactic at all times. 
As regards phototropism and photopathy, the fundamental fact is that the 
snails remain quietly at rest or sealed up by a mucous secretion during bright day- 
light. The ground snails seek the darkness underneath stones and other objects. 
Those that are arboreal come to rest underneath leafy surfaces, and are thus neg- 
atively photopathic. Yet it is difficult to distinguish between the reaction to 
increased or reduced light-influence and the reaction to varying degrees of humidity. 
Under normal conditions of the latter, Partule resume activity at night and become 
quiet in bright light, in practically 95 per cent of the cases as observed in the labora- 
tory, and in experiments in the field where snails were placed on suitable plants at 
the coast for the determination of this point. But if the atmosphere is very dry, 
they are apt to remain sealed up all night, while, on the other hand, if the sky becomes 
clouded and light is reduced, they will crawl about even in the daytime. When 
rain falls and humidity increases greatly, they move about with celerity, crawl to 
the ground, and resume feeding. It is interesting to note that partly grown or 
adolescent snails are much quicker than the adults in their reactions to reduced 
light and to increased degrees of moisture. 
An additional factor of the resultant—quiescence or activity—is the tempera- 
ture. In the field and in the laboratory the snails are brought to rest by a reduction 
of this to 60° F. or 55° F. Naturally, if it is darker and more humid, a still lower 
figure must be reached in order to bring the snail to rest; increase of temperature 
beyond the average by itself does not affect the snails, but greater heat 1s usually 
experienced during the daylight, when the latter acts as an inhibiting factor. 
While the mating habits of snails can rarely be observed, owing to their noc- 
turnal life, several pairs have been found 7m coitu in the daytime, when heavy rains 
were falling. Although the animals are hermaphrodite, it is certain that fertiliza- 
tion is not mutual; one acts as the male and the other as a female. In studying 
the conditions of preserved snails in the course of analyzing the collection, it appears 
that the male generative organs are larger in those individuals that bear no eggs or 
embryonic young; hence it seems probable that the hermaphrodite animals are 
alternately male and female in their virtual constitution and activities. Yet the 
number of gravid snails is almost always more than half of the total number taken 
from one valley, so that an acting male must fertilize a number of other snails, or 
else an impregnated individual may function as a male during the development of 
its embryonic contents. 
