REPROD UCTION 



43 



Indirect nuclear division. The indirect division which occurs 

 in Protozoa is of manifold types as compared with the mitosis 

 in the cells of Metazoa, in which, aside from minor variations, 

 the change is of a uniform pattern. There are, however, in- 

 stances of indirect nuclear division in Protozoa which are similar 

 to the typical mitosis of multicellular animals. Chatton, Alexei- 

 eff and others have proposed several terms to designate the 

 various types of indirect nuclear division, but no one of these 



Fig. 17 Stages in macronuclear division in Uroleptus mohilis. X300. (After 



Calkins). 



a. A stage in the fusion of the macronuclei; the micronuclei 

 in mitosis. 



b. A much later stage in the macronuclear fusion. 



c. The stage in which the macronuclei became fused into 

 one mass prior to amitosis. 



d. A stage in the amitosis of the macronuclear material. 



types is sharply defined, since there are intermediate forms be- 

 tween any two of them. For our purpose, mention of the chief 

 types will suffice. 



A veritable mitosis was noted by Dobell in the heliozoan 

 Oxnerella maritima (Fig. 19), which possesses an eccentrically 

 located nucleus containing a large endosome and a central 

 granule ("centroplast") from which radiate many axopodia {a). 

 The first sign of the nuclear division is the slight enlargement, 



