Kept rimcntal Embryology. 



upon wh; 



ing become grey in from three quarters of an hour to two 



tidal layer of the ego;, white or dark on opposite poles. The 

 dark colored material of the egg is not confined to the surface 

 of the dark pole, but there penetrates far towards the center 



center of the dark pole. 



When the egg is inclined this darker material rises upward 

 along one side of the sphere, carrying the enclosed white yolk 

 with it. while the heavier white yolk flows down on the other 

 side of the sphere from its forced position to a more normal 

 one. Thus the material normally at the upper pole is brought 

 there again, though covered over still by some superficial 

 white yolk that remains over the white pole, now become 



When this rearrangement takes place at so late a stage that 

 the nucleus is dividing as it rises, then the first plane is not 

 necessarily vertical: gravitation acting only indirectly, while 

 other causes determine the direction of the first cleavage 



Roux 6 had drawn the same inference as to the insignifi- 



HV. Roux B q "• U Q el f die 



