CHAP. 



80 CYTOLOGY 



but when the nuclei of the 2-cell stage are preparing for the next 



S,(A) 



Si(B) 



Differentiation of the germ-track in Ascaris megalocephala univahns. (After Boveri, Fest. f. Kupffer, 1899, 

 and Ergebni'ise. 1004.) A, 2-ceU stage. Dimiaution taking place in the cell Sj, chromosomes intact in P\. 

 B, passage of the 2-cell into the 4-cell stage. In S\, numerous small chromosomes formed by the frag- 

 mentation of the two large ones. The broken-otf ends of the latter are seen outside the equator of the 

 spindle. C, 4-cell stage. !n Sj (A) and S\(B) the cast-out ends of the chromosomes are seen in the cytoplasm. 



D, mitosis which will give rise to the 8-ceU stage. Diminution taking place in Sn, chromosomes intact in Pn. 



E, later embryo, process of diminution now complete. The two original chromosomes are still intact in ^4 

 only. 



mitosis, one of them is marked out from the other by the fact that its 



