MITOSIS 209 



and most important changes of the cell during division were 

 connected with the nucleus. It was shown that the chromatin 

 of the nucleus during vegetative stages is distributed, in the 

 form of granules, on a network of achromatic material called 

 linin (Fig. 88, A) ; that these granules collect and coalesce in one 

 or more spirally wound threads of chromatin called the spireme 

 (Fig. 88, B, c); that these spireme threads divide longitudinally 

 throughout the entire length, and that the double spireme then 

 segments into a number of short double rods called chromo- 

 somes (Fig. 88, D, E) . It was discovered that the number of these 

 chromosomes is always the same in individuals of the same 

 species and in all types of the tissue cells of the same individual. 

 At the same time, it was shown tiHat^the chromosomes collect 

 in the center of a peculiar spindle-formed body, derived from 

 achromatic material of the cell, and having characteristics pecul- 

 iar to itself in the form of centrosomes at the poles of the spindle, 

 with spindle fibers running from one centrosome to the other 

 (Fig. 88, D, E, F). It was found that these centrosomes arise by 

 the division of a single centrosome lying on the periphery of the 

 nucleus, and by separation of the daughter-centrosomes through 

 an arc of 180; also that the nuclear membrane disappears at 

 this time, while new fibers (mantle fibers) grow out from the 

 centrosomes, and connect with the chromosomes. It was seen 

 that the two equal parts of each chromosome then separate from 

 one another, each half going toward one of the two centrosomes, 

 so that the entire mass of chromatin material is equally divided 

 between the two daughter-nuclei which are bounded by new nu- 

 clear membranes (Fig. 89, G, H, I, j) . It was noted, finally, that 

 nuclear division is completed by disintegration of the daughter- 

 chromosomes into the distributed chromatin granules character- 

 istic of the vegetative nucleus, and that, after this nuclear 

 division, the cell body divides by a plane, passing through the 

 center of what was the nuclear division figure. 



This complicated chain of processes with its involved activity 

 of chromatin, centrosomes and spindle fibers was named karyo- 

 kinesis by Schleicher 1878, and mitosis by Flemming 1882, and 

 both names are found in current literature. 



