CH. IX] EXPERIMENTS OF BORX AXD OF ROUX 93 



force was twice as great as the force of gravity. When the 

 box was at the lowermost point in a revolution, the centrifugal 

 force and the force of gravity acted together. When the box 

 was at the highest point in its revolution, then the centrifu- 

 gal force and the force of gravity acted against each other. 

 With the velocity of eighty-four revolutions a minute, the cen- 

 trifugal force was greater than the force of gravity, even at 

 the highest point of a revolution. At the intermediate points, 

 i.e. between the highest and lowest points, the conditions are 

 different for each point, and lie between the two extremes just 

 stated. Under the conditions of the experiment the eggs 

 rotated inside their membranes, so that the black pole turned 

 inward, i.e. toward the axis of rotation, and the white pole 

 turned outward. In other words, the eggs now oriented 

 themselves with regard to the centrifugal force, and not with 

 regard to the force of gravity. Even when the centrifugal 

 force was only half that given above, the eggs still arranged 

 themselves with reference to that force. In the latter case the 

 force of gravity was barely overcome by the centrifugal force 

 at the highest point of the revolution. If a still shorter radius 

 were used, so that at the highest point of the revolution the 

 force of gravity was three times as strong as the centrifugal 

 force, even then the eggs oriented themselves as before, i.e. 

 with the black pole turned toward the axis of rotation. In all 

 of these experiments it will be seen that the centrifugal force is 

 a constant force, while the action of gravity varies in direction 

 at each point in the revolution. If a still shorter radius of the 

 wheel was used, in which case the centrifugal force was still 

 less, then the eggs retained any position that they had when 

 first put into the box. 



All of these different possibilities could be realized at the 

 same time by using a series of tin boxes placed at the proper 

 intervals along a radius of the wheel. "The apparatus, 

 laden with ten to eighteen freshly fertilized eggs, was set in 

 motion. I waited with great interest for the appearance of 

 the first cleavage. It appeared at the normal time and the 

 whole cleavage proceeded in exactly the normal way. A nor- 

 mal blastopore appeared, and the formation of the medullary 

 folds, the brain-folds, and closure of the neural tube, and later 



