Sex / by Patrick Geddes ... and J. Arthur Thomson.

  • Patrick Geddes
Date:
[1914], ©1914
Catalogue details

Licence: In copyright

Credit: Sex / by Patrick Geddes ... and J. Arthur Thomson. Source: Wellcome Collection.

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    inheritance of the offspring, the spermato- zoon also introduces a minute body known as the centrosome, which plays an important part in the subsequent division of the fertilised ovum. (4) It is also certain that the sperma- tozoon acts as a stimulus which sets the egg dividing—or, it may be, removes some in- hibiting factor which was keeping the egg from dividing. In a variety of cases what the sperm does, whether in stimulation or in removing a check, can be replaced artificially, and this in many different ways. The experi- ments of Loeb, Delage, and others have shown that the ova of starfish, sea-urchin, worm, mollusc, fish, and even frog can be made to divide without being fertilised. Alterations in the chemical and physical state of the medium, e. g. the addition of a little magnesium chloride to the sea-water, may replace ordinary fertilisa- tion, at least in so far as setting division agoing is concerned. The artificial stimuli effectively used are very varied—physical, chemical, and mechanical—an electric shock, a superabun- dance of carbonic acid gas, and even a pin- prick. They differ for different kinds of eggs, and even for eggs of the same kind at different stages of ripeness. Perhaps there is some common factor in all the effective stimuli, but what it is remains unknown. According to some experimenters, the egg responds directly to the external stimulus; according to others the artificial conditions do not directly induce segmentation, but modify the intimate condition of the egg in such a way that it becomes auto-parthenogenetic. The second view is suggested by cases in which the