ON THE ENERGETICS OF DIFFERENTIATION, VI

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Abstract
1. The effect of temperature on the rate of oxygen consumption of unfertilized and fertilized eggs of Urechis, Strongylocentrotus, Ciona and Dendraster was investigated. 2. The unfertilized eggs exhibit a rising rate of respiration with time in allfour species. The rise is much more rapid in Strongylocentrotus and in Dendraster than in Urechis and in Ciona. This rise appears to be correlated with the loss of fertilizability on the part of the eggs. 3. Methods of determining the temperature coefficients in such a way as to take into account the general rise (which is a significant factor in prolonged runs) and other variations are described. 4. Only the temperature coefficients for the same temperature intervals are compared, the respiration being determined at two temperatures in each experiment. With Urechis and with Strongylocentrotus eggs, experiments were run at temperatures between 22° and 5°; with Ciona, between 25° and 12°; and with Dendraster, 22° and 12°. The experiments with Urechis and Strongylocentrotus thus included low temperatures at which the fertilized eggs fail to cleave. 5. No significant differences between the temperature coefficients of the respiratory rate of unfertilized and of fertilized eggs of the four animals investigated are found over most of the temperature range in which development is possible. At the lower temperatures, there are differences that are possibly significant, the unfertilized eggs giving consistently lower values. 6. Comparison of the absolute rates of respiration of the unfertilized and fertilized eggs shows in Strongylocentrotus and Dendraster the rise in respiration upon fertilization typical of the echinoids; in Ciona a less than two-fold rise is manifest; in Urechis, the rate may rise considerably, remain constant or decrease slightly, depending upon the particular batch of eggs employed. Eggs from animals kept some time in captivity give lower unfertilized rates and manifest a rise upon fertilization; eggs from freshly collected animals give higher unfertilized rates and no rise or even a slight decrease upon fertilization.

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