Experimental embryology / by Thomas Hunt Morgan.

  • Thomas Hunt Morgan
Date:
1927
Catalogue details

Licence: In copyright

Credit: Experimental embryology / by Thomas Hunt Morgan. Source: Wellcome Collection.

    128/790 page 110
    the needle. On removing the needle it regains its original state. The rays may be pulled out or bent or the whole figure may be given a spiral twist. This result is possible because of the con- sistency of the gel between or rather around the more fluid rays. The latter conform to the bending or twisting of the more solid parts. Extensive tearing of the aster may cause reversal, the entire cell passing from a gel to a sol stage. The physical condition of the egg of Cerebratulus at the time when the polar bodies are forming has also been studied by Fig. 20.—Spindle of the egg of starfish at its maximum development, as seen in the living egg. (After Chambers.) Chambers. When the egg-nucleus breaks down, its place is occu- pied by a clear area in the granular protoplasm. The clear area “flows” towards the pole. In it appears the first maturation spindle. As it elongates hyaloplasm collects around the spindle poies, above which the rays (gel) become more distinct. In this stage the whole structure may be pushed or pulled about by the needle, or the rays twisted into a spiral. As the gelatinized rays reach the gelatinous periphery of the egg the two form a con- tinuous substance. “Division of the nuclear spindle is followed by a reversal of the astral structure to the sol stage. The sol state of the cytoplasm lying immediately under the surface where the polar bodies are to form is so liquid that granules pushing
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