The blood osmotic pressure of the terrestrial isopods Porcellio scaber latr. and Oniscus asellus L., with reference to the effect of temperature and body size

• 1.

  1. The blood osmotic pressure in the terrestrial isopod Porcellio scaber varies inversely with the acclimation temperature (as measured at 3, 23 and 30°C). This species also has decreasing osmotic pressures with increasing size.

• 2.

  2. Between 23 and 30°C smaller animals did not show any difference in their blood oxmotic pressure, while in larger animals the blood concentration remained unchanged between 23 and 3°C.

• 3.

  3. Moulting animals as well as ovigerous females have lowered osmotic pressures. There was no influence of sex on the osmotic value in intermoult animals.

• 4.

  4. The blood concentration of Oniscus asellus was not related to body size when measured at 23°C.

• 5.

  5. Some ecological and metabolic implications of these findings are discussed.