EGG CORTEX IN MORPHOGENESIS
369
or occasional tripling, of the embryo-anlagen is related to new and
abnormal relations of the yolk with the cortex, due to the action of
gravity on the heavy yolk when the egg is forced to remain upside down.
As seen in Figs. 3 and 4, the heavy vegetal yolk flows through the egg
FIG. 3. Flowing of the vegetal yolk through an inverted egg. The upper figure is
drawn from a section and explained by the underlying schema.
from the upper vegetal pole towards the lower animal pole. When yolk
reaches the animal cortex, the pigment is displaced from this part of the
cortex ; and reciprocally, part of the vegetal cortex, which has been
released from the yolk, may become pigmented. Thus, one may find at
both poles white areas where, just as in the normal conditions of the
vegetal pole, vegetal yolk is in close contact with the cortex. Surrounding
those areas there is a light greyish border, similar to, although more
irregular in outline than, the 'marginal zone' of the normal egg. The
extent of animal or white areas may be very different from one egg to
another, depending on its individual viscosity, or on the time given to
the yolk to flow before cleavage.
Penners and Schleip recognized that a dorsal blastoporal lip, leading
369
or occasional tripling, of the embryo-anlagen is related to new and
abnormal relations of the yolk with the cortex, due to the action of
gravity on the heavy yolk when the egg is forced to remain upside down.
As seen in Figs. 3 and 4, the heavy vegetal yolk flows through the egg
FIG. 3. Flowing of the vegetal yolk through an inverted egg. The upper figure is
drawn from a section and explained by the underlying schema.
from the upper vegetal pole towards the lower animal pole. When yolk
reaches the animal cortex, the pigment is displaced from this part of the
cortex ; and reciprocally, part of the vegetal cortex, which has been
released from the yolk, may become pigmented. Thus, one may find at
both poles white areas where, just as in the normal conditions of the
vegetal pole, vegetal yolk is in close contact with the cortex. Surrounding
those areas there is a light greyish border, similar to, although more
irregular in outline than, the 'marginal zone' of the normal egg. The
extent of animal or white areas may be very different from one egg to
another, depending on its individual viscosity, or on the time given to
the yolk to flow before cleavage.
Penners and Schleip recognized that a dorsal blastoporal lip, leading