MORPHOLOGICAL COMPOSITION OF THE NUCLEUS 



295 



by extremely strong evidence, derived especially from a study of ab- 

 normal variations in the early development of Ascaris, the force of 

 which has, I think, been underestimated by the critics of the hypothesis. 

 Some of this evidence may here be briefly reviewed. In some cases, 

 through a miscarriage of the mitotic mechanism, one or both of the 

 chromosomes destined for the second polar body are accidentally left 



D 



Fig. 143. Evidence of the individuality of the chromosomes. Abnormalities in the fertiliza- 

 tion of Ascaris. [BOVERI.J 



A. The two chromosomes of the egg-nucleus, accidentally separated, have given rise each to a 

 reticular nucleus ($, 9) \ the sperm-nucleus below (d 1 ). B, Later stage of the same, a single 

 chromosome in each egg-nucleus, two in the sperm-nucleus. C. An egg in which the second 

 polar body has been retained ; p,b? the two chromosomes arising from it ; $ the egg-chromo- 

 somes ; cf the sperm-chromosomes. D. Resulting equatorial plate with six chromosomes. 



in the egg. These chromosomes give rise in the egg to a reticular nu- 

 cleus, indistinguishable from the egg-nucleus. At a later period this 

 nucleus gives rise to the same number of chromosomes as those that 

 entered into its formation, i.e. either one or two. These are drawn 

 into the equatorial plate along with those derived from the germ- 

 nuclei, and mitosis proceeds as usual, the number of chromosomes 

 being, however, abnormally increased from four to five or six (Fig. 143, 



