The Process of Fertilization in the Eggs of the Sea Urchin, Hemicentrotus Pulcherrimus

The process of fertilization was studied in the eggs of the sea urchin, Hemicentrotus pulchernmus. As reported previously, the unfertilized eggs were first immersed in hypotonic sea water, then centrifugalized by an ordinary driven electric centrifuger. By the centrifugation, the egg was remarkably stratified into definite three layers, oil droplets in the centripetal side, clear hyaloplasmic and dark layers in the centrifugal side, respectively. In the case of the sperm attachment at the site of the hyaloplasmic layers, the behavior of the spermatozoon in the process of invasion, and the course of penetration through the egg cortex were precisely reported below.