DISTRIBUTION BY ENVIRONMENTS
preference is accounted for by the relative strengths of the plants'
digestive fluids, but a more probable solution is to be found in the
distribution of the glands within the pitcher which produce the fluid.
In the first, these glands leave off abruptly halfway up the pitcher; in
the third, the glands extend up to the top; in the second, we have an
intermediate arrangement where the glands become progressively less
as the top is approached. Thus in
the spider can sit on a
surface free from digestive fluid.
If the spider is disturbed it slides down on a thread below the
surface of the digestive liquid, and remains there for a period of a few
minutes before regaining its former position. Examination shows that,
in contrast to other Thomisids, its body is encased in a strong
chitinous armour. This protects it from the digestive effects of the
fluid except for a small space on the central surface of the abdomen
around the tracheal spiracle, which is clothed with fine hairs. When
the spider submerges itself these hairs entrap a small bubble of air. In
addition the lung book openings protrude to an extent which is
unusual amongst spiders, and in this manner they also succeed in
storing a small reserve supply of air. When the spider emerges from
the plant fluid it rubs its mouth several times against the sides of the
pitcher to remove the unpleasant taste, but otherwise shows no sign of
Here, then, we have an example of a spider which is adapted both in
habits and in structure to life on one kind of plant. Fage (1930) has
described a second Thomisid,
which has acquired an identical habit, and a Theridiid,
from Madagascar which spins its web within the pitchers.
It is not always easy to differentiate between soil preferences and
preferences for the plants which grow on particular soils. Nevertheless
in a general way one