236 THE CELL 



shorter and thicker (Fig. 125 II., III.). The centrosomes separ- 

 ate from one another, until finally they are situated at oppo- 

 site sides of, and at some distance from, the vesicular nucleus. 

 By this time, the rest of the nucleolus has disappeared; the 

 nuclear membrane becomes dissolved, and the two bundles, each 

 containing four nuclear segments, arrange themselves in the 

 equator between the centrosomes; then each bundle splits up 

 into two daughter-bundles containing two nuclear segments, 

 which separate and move towards the poles (Figs. 125 IV., 

 126 L). The sperm-mother-cell now becomes constricted into 



III. 



Fis. 126. Diagram showing the development of sperm-cells from a sperm-mother-cell 

 of Ascaris megaiocephala livalens. I. Division of the sperm-mother-cell into two sperm- 

 daughter-cells. IT. The two sperm-daughter-cells (A, B) immediately prepare to divide 

 a second time. III. The sperm-daughter-cell A divides into two grand-daughter-cells. 

 B and C are grand-daughter-cells, which have been produced by the division of the 

 daughter-cell B of Fig. IT. 



two daughter-cells of equal size (Fig. 126 II.). Whilst this 

 process of constriction is taking place, the changes commence 

 which lead up to the second division (Fig. 126 I.), the cen- 

 trosome of each daughter-cell splits up into two parts which 

 travel, each surrounded by its own radiation sphere, in opposite 

 directions, which are parallel to the first division plane (Fig. 126 

 A, B). The nuclear segments produced by the first division 

 immediately afford the material for the second division, without 

 passing through the vesicular resting condition. They move 

 until they are situated between the newly-developed poles of the 

 second division figure (Fig. 126 II., J5), and then divide into two 

 groups, each of which contains two nuclear segments ; these groups 

 then separate, and move towards the poles, after which the second 

 constriction commences (Fig. 126 III., A). Whilst after the first 

 division each daughter-cell contains four of the eight nuclear 

 segments, which have developed beforehand in the resting nucleus, 

 each grand- daughter- cell contains only two. For, in consequence 



