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Abstract
The eggs of marine invertebrates particularly the echinoderms as sea urchins sand dollars and starfish are used for the study of fertilization. The specific recognition of the egg by the sperm is thought to occur when the sperm makes contact with the jelly coat that surrounds the egg. Substances in the jelly coat interact with the outer membranes of the sperm cell to release digestive enzymes that enable the sperm to dissolve a hole in the layers surrounding the egg so that the sperm can reach the surface of the egg. A single fertilizing sperm enters the egg. Once the sperm has entered the egg its nucleus rotates 180 degrees and migrates toward the nucleus of the egg. About 20 minutes later paternal and maternal nuclei fuse. With the condensation of the chromosomes and the 1st cleavage of the egg fertilization is completed. The fusion of a sperm and an egg triggers a series of transient changes in the concentration of ions that prevent the fusion of additional sperm and initiate development of the embryo. It seems likely that regulation through the transient or permanent modulations of ionic content is widespread in the living world and that mechanisms for regulating cellular acivity at fertilization are utilized throughout the life span of the organism.
Published Version
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