Abstract
THE popularity of problems of genetics as subjects for research and discussion is well illustrated by the May number of the American Naturalist (vol. xlix., No. 581), every paper in which bears on one or other of such problems. Of especial interest is Prof. Jacques Loeb's article on the nature of the conditions which determine or prevent the entrance of the spermatozoon into the egg. It is well-known that in normal fertilisation, the entrance of the spermatozoon is followed by the formation of a membrane around the egg, so that the entrance of other spermatozoa is prevented. But, as Prof. Loeb has already recorded in his work on “Artificial Parthenogenesis and Fertilisation,” sea-urchin eggs the development of which has been started by treatment with hypertonic sea-water can be afterwards fertilfsed, a spermatozoon being capable of entering a blastomere-at least up to the stage of the eighth cleavage-and inducing “a distinct and clear membrane formation “around it. This shows that the entrance of a male cell is not necessarily prevented by “the changes underlying development.” But eggs by treatment with butyric acid can be induced to form a membrane. If this membrane remain unbroken subsequent fertilisation becomes impossible, though parthenogenetic segmentation may begin; if, however, the membrane be ruptured by shaking, a spermatozoon can enter and the egg undergoes normal development. Hence it may be inferred that the physical condition of the surface of the egg-howsoever modified-is the immediate determinant of the admission or exclusion of a spermatozoon. This view is supported by Loeb's experiments in cross-fertilisation, which show that the sea-urchin (Strongylocentrotus) egg admits the sperm of an echinoderm of another class only in a hyper-alkaline solution. On the other hand, eggs cannot be fertilised by sperms of their own species in sea-water containing an excess of neutral chlorides. From all these facts Loeb is inclined to draw the conclusion that the tension of the surface of the egg may explain the engulfment or exclusion of the spermatozoon. But it is obvious that in the case of normal fertilisation this surface-condition is “induced from within the egg by changes caused by the entrance of the spermatozoon a deduction made by biologists long before the study of “experimental embryology” had become fashionable.
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C., G. The Study of Heredity. Nature 95, 657–658 (1915). https://doi.org/10.1038/095657a0
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DOI: https://doi.org/10.1038/095657a0