Ii6 



THE POPULAR SCIENCE MONTHLY 



to see that each chromomere divides through its middle. The daughter 

 chromosomes then separate and move to opposite poles of the spindle, 

 where they form the daughter nuclei, and at the same time the cell 

 hody begins to divide by a constriction which pinches the cell in two 



Fig. 26. Successive Stages in the Cleavage or the Egg of Holldsk (Crepi- 

 dula), showing the separateness of the male and female chromosomes (J 1 ch, O ch) 

 and the male and female halves of each nucleus (^N, $N). 



in the plane which passes through the equator of the spindle (Tig. 

 26 B). Finally the daughter nuclei grow in size by the absorption of 

 achromatin from the cell body and the substance of the chromosomes 

 is again distributed through the achromatin in the form of threads 

 and granules and thus the daughter nuclei come back to a "resting'' 

 stage similar to that with which the division began, thus completing 

 the " division cycle " of the cell. 



During the whole division cycle it is possible in a few instances to 

 distinguish the chromosomes of the egg from those of the sperm, and in 



