THE MECHANISM OF MITOSIS 



that during the mitosis of various tissue-cells of the salamander, the 

 granules of the spireme-thread divide by fission and thus determine the 

 longitudinal splitting of the entire chromosome. This discovery was 

 confirmed by Flemming in the following year ('82, p. 219), and a simi- 

 lar result has been reached by many other observers (Fig. 54). The 

 division of the chromatin-granules may take place at a very early 

 period. Flemming observed as long ago as 1881 that the chromatin- 



Fig. 55. Formation of chromosomes and early splitting of the chromatin-granules in sperma- 

 togonia of Ascaris megalocephala, var. bivalens. [BRAUER.] 



A. Very early prophase; granules of the nuclear recticulum already divided. B. Spireme; 

 the continuous chromatin-thread split throughout. C. Later spireme. D. Shortening of the 

 thread. E. Spireme-thread divided into two parts. F. Spireme-thread segmented into four split 

 chromosomes. 



thread might split in the spireme-stage (epithelial cells of the sala- 

 mander), and this has since been shown to occur in many other cases ; 

 for instance, by Guignard in the mother-cells of the pollen in the 

 lily ('91). Brauer's recent work on the spermatogenesis of Ascaris 

 shows that the fission of the chromatin-granules here takes place even 

 before the spireme-stage, when the chromatin is still in the form of a 

 reticulum, and long before the division of the centrosome (Fig. 55). 

 He therefore concludes : " With Boveri I regard the splitting as an 



