7S 



CELL-DIVISION 



''ail independent vital manifestatio)i, an act of reproduction on the part 

 of the cJiroviosoines.'" ^ 



All of the recent researches m this field point to the conclusion 

 that this act of division must be referred to the fission of the 

 chromatin-granules or chromomeres of which the chromatin-thread 

 is built. These granules were first clearly described by Balbiani 

 {^'j6) in the chromatin-network of epithelial cells in the insect- 

 ovary, and he found that the spireme-thread arose by the linear 

 arrangement of these granules in a single row like a chain of bacte- 

 ria." Six years later Pfitzner ('72) added the interesting discovery, 

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

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



Fig. 38. — Nuclei in the spireme-stage. 



A. From the endosperm of the Hly, showing true nucleoli. [Flemming.] 



B. Spermatocyte of salamander. Segmented double spireme-thread composed of chromo- 

 meres and completely split. Two centrosomes and central spindle at s. [HERMANN.] 



C. Spireme-thread completely split, with si.\ nucleoli. Endosperm of Fritlllaria. [Flem- 

 ming.] 



lon^i^itudinal splitting of the entire chromosome. This discovery was 

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

 ilar result has been reached by many other observers (Fig. 38). The 

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

 period. Flemming observed as long ago as i88r that the chromatin- 

 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 Asearis 

 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 



i'88, p. 113. 



2 See '81, p. 638. 



