MITOSIS 



107 



multiplication in species of Aggregata, as described by Moroff (1908) 

 and other observers (Fig. 63). 



The main types of nuclear divisions of Protozoa may be thus 

 classified : 



1. Mitotic division with centrosomes, asters, achromatic spindle, 

 chromosomes, equatorial plates, and all the stages seen in the typical 

 nuclear division of higher animals. The nuclear membrane may or may 

 not persist during division. A nucleolus or plastin body, if present, may 

 be divided into two parts, one of which goes to each daughter nucleus, 

 or it may break up and disappear, the daughter nuclei re-forming their 

 nucleoli when division is approaching completion. 



Fig. 63. — Poly-aster Figure resulting from Successive Nuclear Divisions 

 IN Male Gametocyte of Aggregata jacquemeti ( x 750). (From Minchin, 1912, 



AFTER MOROFF.) 



2. Mitotic division of the above type, except that centrosomes and 

 asters have not been detected. 



3. Division in which there is formed within the nuclear membrane 

 a spindle upon which chromatin granules are irregularly arranged. There 

 are no asters or centrosomes. It is possible that the granules of chromatin, 

 though not arranged as an equatorial plate, are actually chromosomes, 

 which divide into daughter chromosomes as they do in the preceding 

 types of division. The karyosome may divide into daughter karyosomes, 

 or break up to be re-formed in the daughter nuclei, 



4. Division in which the large central karyosome elongates and becomes 

 constricted. The two halves move to the ends of the elongating nuclear 

 membrane to form the pole caps between which a spindle is formed. 

 The peripheral chromatin becomes arranged as chromosomes in an 



