The Distribution of Po2 and Hydrostatic Pressure Changes Within the Branchial Chambers in Relation to Gill Ventilation of the Shore Crab Carcinus Maenas L

Abstract

ABSTRACT Many studies have been made of the mechanisms which maintain the flow of water across the gills of aquatic animals. In no case, however, has it been possible to formulate a detailed account of the path of the water and blood relative to one another at the exchange surfaces. One of the reasons for this is because the gills are usually contained within enclosed cavities and also they may move during the ventilation cycle. The situation is more complicated as the walls of the branchial cavities may also be involved in the ventilation movements, as, for example, the operculum of teleost fishes. The further detailed analysis of gaseous exchange at gills, which is best known in fishes, has been held up because of the lack of information of this kind. The study of gill ventilation in the Crustacea has distinct advantages from this point of view. The wall of the branchial chamber is rigid and a window can therefore be fixed in it without disrupting the normal hydrodynamic conditions. Furthermore, the rigid exoskeleton allows the animal to be held in a fixed position, and it provides a site for the attachment of recording leads and water-collecting tubing. Another advantage is that the gills of these animals do not move during a normal respiratory cycle. Much work has been carried out on the ventilation of decapod Crustacea but few studies (e.g. Larimer, 1964) have made use of modern pressure recording equipment and oxygen electrodes.