Fertilization of the Egg
Nature uses varied means to bring egg cells and sperm cells together. Sea urchins and many other marine animals release into the water such an enormous number of gametes that random chance alone suffices to bring about the necessary encounter. The eggs do release into the surrounding water special substances (fertilizins) which affect the sperm, changing their surfaces in a way which enables them to penetrate the egg. But no one has been able to demonstrate that these egg substances directly attract the sperm. Indeed, within the animal kingdom such a chemotaxis (p. 104) has been proved only in the case of the marine hydroid Campanularia.
KeywordsMold Tempo Hydroid Thioglycolate
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