ON THE ENERGETICS OF DIFFERENTIATION. VII COMPARISON OF THE RESPIRATORY RATES OF PARTHENOGENETIC AND FERTILIZED URECHIS EGGS ALBERT TYLER AND N. H. HOROWITZ (From the William G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena, California) The results of these experiments show that the rise in respiratory rate that occurs during development is correlated with cleavage; eggs that fail to cleave after activation show a greatly retarded rise while those that cleave show a rise that is roughly commensurate with their division rate. Inhibiting cleavage with phenylurethane affects the respiratory rate similarly. THEORETICAL PART It has been long been known that the rate of respiration rises during development. This increase in rate is evidently not directly propor-tional to the increase in the number of cells (cf. Needham, 1931). It might, nevertheless, depend upon changes in the egg brought about by cell division, so that when cleavage fails to occur the rise in respiration would be inhibited. We have considered in previous work the dependence of the form-changes on the respiration, the rate of oxygen consumption being taken as a measure of the energy available for the various developmental processes. We consider now the possibility that the developmental changes determine in turn the rate of respira-tion. If, for example, early cleavage is inhibited in a manner that does not affect the absolute rate of respiration at the particular stage, then we may expect, on this basis, failure of the subsequent rise. In the early work of Warburg (1910) it has been shown that cleav-age could be suppressed in sea urchin eggs by means of phenylurethane without immediately affecting the respiratory rate. However, the question of whether or not the rate would rise later was not investigated. Also it has been shown that after parthenogenetic activation of sea urchin eggs the same increase in rate occurs that is obtained normally upon fertilization (Warburg, 1910; Loeb and Wasteneys, 1913). But here again it would be desirable to know what happens later, especially since the parthenogenetically activated eggs develop much more slowly in general and often stop in early cleavage or even fail to divide. 99
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