458 



WILSON. 



[Vol. XI. 



where in some cases only a fraction of tlie chromatic substance 

 persists as such).^ 



B. Later History of the CJiroviatin. — The rod-shaped chro- 

 mosomes arrange themselves in the equatorial plane of the 

 spindle and split lengthwise in the typical manner. Diver- 

 gence of the daughter-chromosomes always begins at the inner 

 end (towards the axis of the spindle) and proceeds thence out- 

 wards, the chromosome assuming meanwhile the form of a Y, 

 the final separation taking place at the outer end, and the 

 daughter-chromosomes of each pair lying end to end. (Text- 

 fig. VII. A photograph will be elsewhere published.) The 

 daughter-chromosomes move rapidly apart and finally pass to 



Fig. VII. — Metaphase. Splitting of the chromosomes and divergence 

 of the daughter-halves. 



the extreme limit of the spindle, where they lie immediately 

 in contact with the reticular centrosphere (Phototype 8, Text- 

 fig. VIII, A). Each of them is now converted into a small 

 spherical vesicle filled with a clear, unstained substance, the 

 chromatic substance forming the wall of the vesicle, and often 

 being aggregated more especially at one side (Phototype 9, 



1 This was shown many years ago by Fol in the case of the echinoderm egg 

 (Recherches sur la Fecondation, etc., Mem. Soc. Phys. et d'Hist. nat. de Geneve, 

 1879), 3-nd has been observed by a number of observers since. In the starfish 

 Asterias, according to Mathews (Journal of Morphology, X, p. 334) by far the 

 larger part of the chromatin is discharged from the germinal vesicle and converted 

 into cytoplasm, an observation I can confirm, from a study of the original prepa- 

 rations, which show that at least nine-tenths of the chromatin is thrown out. 

 The same is true of the acoelous Turbellarian, Polychoerus caudahis, according to 

 unpublished observations of Dr. E. G. Gardiner, who has given me an opportunity 

 to examine his preparations, showing the elimination of the chromatin in the 

 clearest manner. 



