Rhythmic Respiration in the Sea Urchin

I AM much interested in the note by Dr. Erik Zeuthen on the presence of rhythmic respiration in sea urchin eggs¹. Fifteen years ago, while at Harvard, I performed a number of experiments on the fertilized eggs of another species of the sea urchin, Arbacia punctulata, using the Warburg microrespirometer technique. I found rhythmic variation in the rate of oxygen consumption by these more or less uniformly cleaving eggs. The phenomenon is quite pronounced at 25°, but not so at 15°. The oxygen consumption ν. time, or oxygen consumption ν. cleavage curves are very much the same as those given by Dr. Zeuthen. I also discussed in detail the reasons for the failure of previous workers to find such variations. In Warburg's first experiments² the readings were taken at too long intervals, and Gray's³ experiments were made at too low a temperature (11°) for the variations to be significant. Shearer's data actually showed such a variation if his data were replotted differentially as rate against time, rather than as an integral curve of amount of oxygen consumed against time, which was the way he plotted the results.