Characteristics of the Utilization of Nucleosides by Embryos of Paracentrotus lividus

Abstract

Embryos-Gametes were obtained from the gonads of sea urchins (P. lividus) collected from the area of the bay of Naples from March to July. The eggs were suspended and washed in filtered sea water. Fertilization was performed by stirring with a small amount of sperm on a glass rod at 20-22”. Fertilized eggs were allowed to develop at 18” in filtered sea water in a constant temperature room, where their containers were tilted rhythmically, or in beakers in a constant temperature bath, in which they were slowly stirred. These conditions allowed development at least to the late pluteus stage. All experiments were performed with suspensions of 5000 embryos per ml. Concentrations of embryos and their stages of development were ascertained at 100 x magnification in a counting chamber. In the experiments on synchronously dividing embryos, two simultaneous samples were taken for biochemical assay and for determining the stage of development. To the former sample was added 5% trichloroacetic acid, to the latter 1% formalin in sea water. The average number of cells per embryo are plotted in Figs. 2, 3, and 4 to show the stage of development. These curves refer to the times at which given numbers of cell divisions are completed, i.e. when the cleavage furrows are completed. Incorporation caused by bacterial contamination may be regarded as negligible, since even in very long incubations of un