ROBERT CHAMBERS 



53 



quickly completed its course in the nucleated fragment (c). Some- 

 what later the cleavage of the non-nucleated fragment (d) was also 

 completed. Fig. 1 e represents a segmenting egg in which the cut 



Fig. 1. A diagrammatic representation of Yatsu's results'* on cutting the 

 segmenting eggs of Cerehratulus. The direction of the cut is shown in a. The 

 original cleavage furrow completed its course in the nucleated fragment c at the 

 same time that it persisted in the non-nucleated fragment h. The furrow finally 

 cut through the non-nucleated fragment in d. In e a cut was made across one 

 end of the segmenting egg. The original furrow completed its course in / re- 

 sulting in two unequal blastomeres. 



was made at one end of the egg at right angles to its long axis. The 

 original furrow persisted so as to divide the mutilated egg into two 

 unequal blastomeres (/) . 



My cutting experiments were carried out mostly on the starfish 

 egg, as sea urchins were very scarce during the summer of 1918. 



