ROBERT CHAMBERS 



55 



in two in a plane diagonal to the cleavage furrow. The fresh surfaces 

 caused by the cutting form films which prevent reunion of the pieces. 

 The egg was in this way cut into two pieces each consisting of egg 

 substance lying on both sides of the cleavage furrow. 



4.20 



Ar.^0 



5.00 



Fig. 3. Effect of a diagonal cut through an Asterias ovum beginning to segment 

 in which the cut did not disturb the physical state of the ovxim. a, operation 

 performed at 4.15 p.m. b, 4.20 p.m., persistence of cleavage furrow in the original 

 plane, c, 4.40 p.m., non-nucleated fragments pinched off. d, 5.00 p.m., 

 nucleated fragments have segmented. 



On one occasion the operation was performed on twelve eggs. In 

 nine cases the original cleavage plane was maintained so that each 

 piece pinched off a non-nucleated fragment normally belonging to 

 the other blastomere. Two of them are illustrated in Figs. 3 a to d 

 and 4: ato d. 



