DISTRIBUTION BY ENVIRONMENTS 

109

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 

N

.

 gracilis 

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 

distress. 

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, 

Thomisus nepenthiphilus

,

from Sumatra 

which has acquired an identical habit, and a Theridiid, 

Theridion 

decaryi

,

from Madagascar which spins its web within the pitchers. 

SOIL PREFERENCES. 

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