?oo 



SOME PROBLEMS OF CELL-ORGAXIZATION- 



alniost no direct evidence exists to show that the chromosomes persist 

 as " individuals " in the chromatin-reticulum of the resting cell. The 

 facts indicate, on the contrary, that in the vast majority of cases the 

 identity of the chromosomes is wholly lost in the resting nucleus, and 

 the attempts to identify them through the polarity or other morpho- 

 logical features of the nuclear network have on the whole been futile. 

 It is therefore an abuse of language to speak of a persistent " individ- 



B 



C 



Fig. 147. — Hybrid fertilization of the egg oi Ascaris megalocephala, var. bivalens, by the sper- 

 matozoon of var. univalens. [Herla.] 



A. The germ-nuclei shortly before union. B. The cleavage-figure forming ; the sperm-nucleus 

 has given rise to one chromosome (cf), the egg-nucleus to two (9). C. Two-cell stage dividing, 

 showing the three chromosomes in each cell. D. Twelve-cell stage, with the three distinct chro- 

 mosomes still shown in the primordial germ-cell or stem-cell. 



uality "' of chromosomes. But this verbal difficulty should not blind 

 us to the extraordinary interest and significance of the facts. It is 

 difficult to suppose that the tendency of the chromatin to resolve 

 itself into a particular number of chromosomes is directly due to its 

 chemical or molecular structure, or is analogous to crystallization ; for 

 in the chromatin of the same species, or even in that of the same ^gg, 

 this tendency varies, not with chemical, but with purely morphological 



