ELEMENTS OF MICROBIAL CYTOLOGY 



33 



the centriole (Fig. 21, A,b, c), and the two resulting centriole- threads 

 pass to the extremities of the achromatic spindle, while the karyosome 

 cooperates in the formation of the chromosomes (Fig. 21, A, d, e). 



In other cases (various fungi, Gregarina, etc.), the centriole be- 

 comes extranuclear, and the karyosome acts as a true nucleolus (Fig. 



a b c y 



a e 





:>c 







^- 



L 



-J 



Fig. 21. — Mesomitosis. A, In Pelomyxa palustris. (a) Nucleus at rest; (6) 

 —(e) division of centriole; (/) (g) equatorial plate; (A) anaphase. (After Bot^.) 

 B, In Urospora lagidis {Gregarina). (a) Nucleus with extranuclear centriole and 

 aster- (6) the centriole is divided and the spireme is formed; (c) spireme; (d) equa- 

 torial plate; (e) anaphase. {After Brasil.) C, In the ascus of GalacHma succosa 

 {Ascomycete). (a) Equatorial plate; (6) anaphase; (c) telophase. 



21). Sometimes it dissolves at the beginning of mitosis, seeming to 

 aid the development of the chromatin of the spireme, and sometimes 

 it persists during the entire process and is expelled in the cytoplasm 

 at the end of the phenomenon without any known function. The 



