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LECTURES ON BIOLOGY 



this time there is no longitudinal fission of the chromosomes ; 

 division proceeds forthwith, and into each of the cells forming 

 only two chromosomes are introduced. With that the maturing 

 of the germ-cells is complete, and each of the four spermatids 

 is transformed into a complete spermatozoon which has in its 

 head-nucleus only half the chromatin of the body-cells of the 

 nematode. 



In much the same manner proceeds the maturing of the 

 egg-cells, only that here instead of four equivalent cells, one large 

 cell, the ovum proper, and four small cells are formed. The 



FIG. 72. DIAGRAM OF A MATURATION DIVISION. 



(1) Spermatocyte of first order. 2-4 first maturation division ; (5) second 

 maturation division ; (6) the resulting four germ-forming cells, with the nuclear 

 loops reduced by one-half, and changed immediately into spermatozoa. (The 

 maternal and paternal nuclear loops are indicated by white and black squares 

 respectively. 



latter are the so-called 'directive-bodies' which soon perish. 

 We begin again with the grandmother of the matured ovum, the 

 oocyte of the first order. Here, too, the chromosomes have 

 doubled before the division began, and arranged themselves in 

 two groups of four. Now the nucleus moves to the margin of 

 the cell, the dividing apparatus begins to act, and four chromo- 

 somes remain in the ovum, while a small quantity of protoplasm 



