ON THE ENERGETICS OF DIFFERENTIATION. III

COMPARISON OF THE TEMPERATURE COEFFICIENTS FOR CLEAVAGE AND LATER STAGES IN THE DEVELOPMENT OF THE EGGS OF SOME MARINE ANIMALS

¹ From the William G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena, California

The effect of temperature on the rate of development of eggs of Ciona intestinalis, Dendraster excentricus, Urechis caupo, Strongylocentrotus purpuratus and Lytechinus anamesus has been investigated. It is found that not only do the various early cleavage stages have the same temperature coefficient, but the values for the later stages of differentiation are the same as for cleavage.

In Ciona, the coefficient for hatching time is different from that for cleavage. An interpretation of this based on the production and diffusion of a hatching enzyme is suggested.

Counts of the number of cells of gastrulæ of Strongylocentrotus show no significant differences in embryos raised at different temperatures.

The data are fairly well expressed by the assumption of a linear relation between the rate of development and temperature.

The values of the coefficients for all the forms investigated, with the exception of Strongylocentrotus, are very closely alike, although the rates of development are quite different. Strongylocentrotus eggs, which develop more slowly than Dendraster or Lytechinus, give lower values of the temperature coefficient.