56 



PROTOPLASMIC CONSISTENCY AND CELL DIVISION 



In one case the cut was made at 4.15 p.m. (Fig. 3 a). 5 minutes 

 later the cleavage furrow had progressed in the original plane (Fig. 

 3 b). At 4.40 it had completed its course so that each piece was 

 divided into a small non-nucleated and a large nucleated fragment 



Fig. 4. Similar operation to that shown in Fig. 3 except that the diagonal cut 

 is more nearly perpendicular to the cleavage plane with the result that larger 

 non-nucleated fragments are pinched off by the cleavage furrow. 



(Fig. 3 c). At 5 p.m. each of the two nucleated fragments or blasto- 

 mere remnants had divided once (Fig. 3d). 1 hour later they had 

 divided once again. By the next morning the egg developed into a 

 double blastula with the two non-nucleated fragments lying as inert 

 masses within the fertilization membrane. 



