Experimental Study of Fertilisation

Abstract

IN 1898 Prof. Yves Delage made a remarkable experiment.¹ He divided the unfertilised egg of a sea-urchin (Strongy-locentrotus lividus) under the microscope into two parts—one containing the nucleus and the centrosome, the other simply cytoplasmic. Beside these he placed an intact ovum, and then supplied spermatozoa. Towards these the three objects showed equal “sexual attraction”; all three were fertilised; and all three segmented, the intact ovum most rapidly, the nucleated fragment more slowly, the non-nucleated fragment more slowly still. In one experiment, the development proceeded for three days, during which the intact ovum had become a typical gastrula, the nucleated fragment a smaller gastrula, and the non-nucleated fragment a quasi-gastrula with almost no cavity. In each case the cells showed nuclei. The conclusion was then drawn that fertilisation and some measure of development may occur in a fragment of ovum without nucleus or ovocentre, and it was suggested that we have in fertilisation to distinguish two processes:—(a) the stimulus given to the ovum by a specially energetic kinoplasm brought in by the spermatozoon, perhaps in its centrosome; and (b) the mingling of heritable qualities, or amphimixis. One may also note that the experiment was suggestive in furnishing experimental confirmation of what is generally assumed, that each of the sex-cells is a fully equipped potential individuality. Here we may recall the remarkable experiment of H. E. Ziegler,² who divided the just fertilised ovum of a sea-urchin in such a way that each half had one pronucleus, and observed that the half with the male pronucleus segmented and formed a blastula.