No. 593] 



THE EVOLUTION OF TEE CELL 



273 



tive, as well as quantitative, partition of the chromatin- 

 particles. In its perfect form this type of nuclear divi- 

 sion is known as karyokinesis or mitosis, and all stages 

 in its progressive development are to be found in the 

 Protozoa. 



In the evolution of nuclear division by karyokinesis 

 two distinct processes are being developed and perfected 

 in a parallel manner, but more or less independently ; first, 

 the method of the partition and distribution of the chro- 

 matin-grains between the two daughter-nuclei; secondly, 

 the mechanism whereby the actual division of the nucleus 

 and the separation of the two daughter-nuclei are effected 

 in the cell-division. I have dealt elsewhere 27 with the 

 evolution of the mechanism of karyokinesis as exempli- 

 fied by the numerous and varied types of the process 

 found amongst the Protozoa, and I need not discnss the 

 matter further here, but the behavior of the chromatin- 

 grains may be dealt with briefly. The main feature in the 

 process of the exact quantitative and qualitative distri- 

 bution of the daughter-chromatin between the daughter- 

 nuclei is the aggregation of the chromatin-grains or chro- 

 mioles into definite, highly individualize 



known as chromosomes. In the most 



as of 



the process of chromosome-formation the chronuoles he- 

 come united into a linear series termed by Vejdovsky a 

 chromoneme, which is supported upon a non-ehroinatmic 

 basis or axis. According to Vejdovsky, the supporting sub- 

 stance consists of linin ; K. Hertwig, however, in his we 

 known studies on Actinosphcerium 28 considers that the 

 supporting and cementing substance of the chromosome 

 is plastin derived from the substance of the nucleoli. 

 However that may be, the essential feature of the chro- 



- 



of the ehromioles to 



form the chromoneme, a thread of chromatin 

 be disposed in various ways on the supporting 

 times being wound spirally round it (Vejdov 



