Respiratory Movements in Holothuria Forskali Delle Chiaje

Abstract

1. The respiratory rate of Holothuria forskali has been found to be between 0.0162 and 0.0465 ml. O₂/g. dry wt./hr. at 17° C. 2. By separating the water pumped by the cloaca from that in contact with the general body surface it is found that cloacal gas exchange accounts for approximately 60% of the total uptake of oxygen by the animal. 3. Uptake of oxygen through the cloaca occurs only when the pumped water is more than 60-70% saturated with air. At lower concentrations there is no exchange through the respiratory trees and no corresponding increase in absorption through the general body surface. 4. Pumping rhythms in intact H. forskali are described. It is shown that there are three main types. In all types the rate of pumping increases as the oxygen in the pumped water becomes depleted. At concentrations corresponding to 60-70% air-saturation, however, pumping ceases and this coincides with the observed reduction in cloacal gas exchange. 5. It is shown that a period of reduced gas exchange through the cloaca is followed by increased uptake of oxygen when pumping is resumed. 6. Measurements of the coelomic oxygen concentration shows that cessation of pumping is followed by a rise in the oxygen concentration in the coelomic fluid. 7. The function of the coelomic oxygen reservoir is discussed.