The Physiology of Sea-Urchin Spermatozoa

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Abstract
1. Echinus esculentus spermatozoa are normally motionless in undiluted semen. They become active when the semen is diluted with sea water or seminal plasma obtained by gentle centrifugation (1500 r.p.m., 12 cm. radius, for 15 min.). 2. A sperm-immobilizing substance can, however, be obtained in seminal plasma by more prolonged centrifugation of semen. 3. Spermatozoa can be made motile in undiluted semen by increasing the O2 tension in the atmosphere surrounding the semen. 4. This O2 activation is completely inhibited by N2; the N2 effect is reversible. 5. Measurements of seminal O2 tension were made with an O2 electrode. The O2 tension of semen is low, being at most 15 mm. Hg. It was not possible to decide whether this residual tension was due to O2 or some other substance reacting at the electrode. 6. The K content of seminal plasma is about 1·55 mg./ml., which is four times higher than that of perivisceral fluid or sea water. 7. The pH of semen is lower than that of sea water, being approx. 7·5. 8. Neither K concentration nor pH is responsible for the inactivity of sperm in semen. 9. A hormone, Androgamone I, is often considered to be responsible for the inactivity of spermatozoa in non-mammalian semen. No support has been found for this view and it is concluded that in E. esculentus semen the spermatozoa are motionless through lack of O2.