ON THE ENERGETICS OF DIFFERENTIATION. III

Abstract

3. The rates of attainment of the various early cleavage stages and of the later stages in the development of the eggs of certain marine animals are found to have the same temp. coefficients. Eggs of Ciona intestinalis, Dendraster excentricus, Urechis caupo, Strongylocentrotus purpuratus, and Lytechinus anamesus were investigated. The coefficient for hatching in Ciona is different from that for cleavage. No significant differences are found in the number of cells in gastrulae of Strongylocentrotus raised at different temps., which is to be expected if the later cleavage stages have the same temp. coefficient as the earlier ones. The assumption of a linear relation between rate of development and temp. expresses the data fairly well. 4 of the forms investigated have very similar temp. coefficients although the rates of development are quite different. In the 5th, Strongylocentrotus, the temp. coefficient is much lower than in the others.[long dash]4. The total oxygen consumed in reaching the same stage of development at different temps. is the same. The measurements with Strongylocentrotus eggs were made in the early cleavage and gastrula stages as well as throughout all those stages and at 20[degree], 15[degree], 10[degree] and 7.5[degree]C; with Dendraster, in the early cleavage, blastula and gastrula stages as well as continuously throughout those stages, and at 25[degree], 22[degree], 20[degree], 15[degree] and 12[degree]C; with Urechis, in the early cleavage stages, and at 22[degree], 20[degree], 15[degree] and 12[degree]C; with Ciona, in the early cleavage stages and up to hatching, and at 20[degree] and 15[degree]C. An exception appears in 1 expt. with Dendraster in which the total respiration at 25[degree] is higher than at 15[degree]C. Aside from this case, the results show that no optimum temp. exists at which development is accomplished with a minimum oxygen consumption.