Abstract
1. The present study deals with the role of the rectal bladder of spiders in the water conservation.
2. In the experiments, adult females of the following species were used: Araneus ventricosus (L. KOCH), Nephila clavata L. KOCH and Agelena opulenta L. KOCH.
3. The contents in the intestine, Marpighian tube and rectal bladder of spiders bred in the different conditions were compared. The influences of starvation and humidity on the osmotic pressure of the blood and the rectal bladder fluid were investigated.
4. It was recognized that the liquid part in the rectal bladder decreased and the osmotic pressure increased more than that of blood did in accordance as the days of starvation increased and humidity lowered.
5. The results obtained seem to suggest that the rectal bladder plays a role of the active reabsorption of water.
