The role of the haemolymph in the carbohydrate metabolism of Carcinus Maenas

The importance of the blood in crustacean metabolism was first raised by Johnston, Davies & Elder in 1971. Until then the conventional view had been that the crab hepatopancreas had a role similar to that of the vertebrate liver (Vonk, 1960), the blood presumably acting as a carrier of soluble sugars. It has recently been shown, however, that blood tissue holds almost four times the amount of polysaccharide than the hepatopancreas and that glucose is actively incorporated into glycogen in the blood (Johnston & Davies, 1972). Polysaccharides were located in deposits in the haematocytes (Johnston, Elder & Davies, 1973). Many previous studies have shown that the main plasma sugar, glucose, varies widely in concentration and appears very sensitive to the animals physio-logical state (see Hohnke & Scheer, 1970). It would seem, therefore, that glucose metabolism in crabs may be readily modified and that by looking at the effect of a physiological stress (starvation and feeding) on the blood/hepatopancreas system one might get some information on the dynamic relationship between these two organs. Previous work (P. L. Lutz, unpublished) had shown that in Carcinus maenas plasma glucose could fall to negligible values on prolonged starvation.