1. Alma emini, a glossoscolecid oligochaet, is a common inhabitant of the water-logged and often floating mat of decomposing vegetable matter which forms the substratum of the papyrus swamps of East Africa.

2. Oxidation-reduction potential (E7) measurements in the field show that to within a fraction of a centimetre of the surface this material is strongly reducing and is presumably devoid of free oxygen.

3. Alma lives with most of its body immersed in this material, but for much of the time it exposes to the air a tubular ‘lung’ formed by the upfolding of the edges of the highly vascular dorsal surface at the hind-end. On retreating from the surface bubbles of air are often carried down enclosed in this tube.

4. The dissociation curve of the haemoglobin is such as might well fit the animal to this mode of life. In the absence of CO2 it is saturated at about 2 mm. Hg of oxygen.

5. A Bohr effect is not detectable unless the tension of CO2 is raised to about 200 mm. Hg, and even then it is slight. This would also fit it for respiration in a medium in which very high tensions of CO2 must occur.

6. In the laboratory it is unaffected by prolonged exposure to an atmosphere of pure CO2.

7. Though apparently capable in the laboratory of a purely anaerobic metabolism, its behaviour in mud-water cultures suggests that it needs oxygen for survival in its normal environment.

8. The possible functions of aerobic and anaerobic respiration are discussed.

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