Abstract
It has been known that the frog egg on the stage of the second polar spindle-metaphase passes into a resting period, awaiting fertilization. Under natural conditions this lasts for only a few hours, but can be delayed up to 3 days without impairing perceptibly the vigor of the egg. After a further delay of 2 days, however, the eggs are dead. In the interval the eggs gradually lose their capacity to develop into normal embryos. The abnormality of these overripe eggs becomes manifest in the following features.
1. The mechanism of control protecting normal eggs against polyspermy is impaired. As a consequence a high percentage of the overripe eggs show multiple segmentation. 2. In monosperm eggs the animal blastomeres are reduced in size, which effect seems to be due to a change in viscosity of the ovoplasm. 3. In the later development a marked tendency to produce axial duplications and supernumerary appendages is observed. These monstrosities as well as the polyspermy indicate a lack of control and coordination within the embryo and the egg. It probably is due to alterations in the cortical layer of the egg, developed during the time of overmaturing. The appearance of monstrosities during the later embryonic stages proves that such plasmatic changes eventually persist for a long time or even become permanent. 4. In the overripe egg as well as in the cells of the embryo derived from such, one finds an overabundance of light brown pigment granules. 5. The most conspicuous pathological feature is the loss of power of differentiation in the embryonic cells and the tendency to start into neoplastic growth. Concerning this point a few details may be added.
The epidermis is thickened, consists of much enlarged cuboid cells and often by a wild growth gives rise to a characteristic epithelioma.
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