THE REPRODUCTION OF THE PROTOZOA 



109 



plate, which divides into two equally definite daughter-plates com- 

 posed of distinct chromosomes ; whether this division is brought 

 about by splitting of the individual chromosomes is not clear. 

 When the nucleus is finally constricted into the two daughter- 

 nuclei, the chromosomes are at first aggregated close beside their 

 respective karyosomes, but soon distribute themselves in the 

 manner alreadv described. 



/ 



The simple types of mitosis described in the two foregoing para- 

 graphs are examples of the so-called " promitosis " (Nagler, 95) 



FIG. 56. The two methods of nuclear division in Anceba diplomitotica. A, Resting 

 nucleus ; B G, first method ; H K, seconu method. In F and G only 

 one of the two halves of the nuclear figure is drawn. After Aragao (87). 



seen commonly in nuclei of the protokaryon-type. The nuclear 

 membrane in this type is a negligible quantity ; it may be scarcely 

 or not at all developed in the resting nucleus, and when a distinct 

 membrane is present it may vanish entirely during the mitosis, as 

 in the form just described. In any case, however, the entire mitosis 

 goes on within the nuclear space. The chromosomes may show 

 every possible condition in different cases, from complete irregu- 

 larity in form, number, arrangement, and mode of division, to the 



