94 DEVELOPMENT OF THE FROG'S EGG [Cii. IX 



the formation of the suckers, gills, and tail, all took place nor- 

 mally. There was no difference in the time of development 

 between the eggs in the machine and the normal eggs outside," 

 used to check the results. 



In the eggs acted upon by the centrifugal force, the segmen- 

 tation-axis corresponded with the egg-axis, and showed no 

 relation to the direction of the force of gravity. The third 

 furrows appeared nearer to the black pole, and the black cells 

 always divided faster than the white cells, regardless of the 

 position of the egg in respect to the force of gravity. The 

 blastopore appeared in its usual position. 



Roux concluded that Pfl tiger's interpretation of his experi- 

 ments in regard to the action of the force of gravity was in- 

 correct. Roux said that in his own experiment the localized 

 effect of the force of gravity had been done away with, when 

 the eggs were slowly revolved, i.e. in those eggs nearest the axis 

 of the machine, and still the cleavage appeared in these eggs 

 irrespective of their position. When the centrifugal force was 

 stronger, it replaced the force of gravity, and the eggs oriented 

 themselves in regard to the new force, and still the cleavage 

 and the subsequent development took place normally. 



Roux pointed out that a possible objection might be made as 

 to the sufficiency of his results. Since the eggs were always 

 rotated in a constant plane, it might be affirmed that gravity, 

 acting vertically in the plane of rotation, still acted upon the 

 egg. To meet this objection a new experiment was devised. 

 Single eggs were placed in a glass tube 6 cm. long. This tube, 

 only half filled with water, was closed and fastened to the cen- 

 trifugal machine. During each rotation of the apparatus, the 

 eggs and the water would fall from one end of the tube to the 

 other, so that the orientation of the eggs would be changed 

 during each revolution. Nevertheless embryos normal in 

 structure were produced. They were, however, small and 

 weak. 



