Reduction in the Protozoa 



183 



Protozoa as in the ciliate infusoria. In the gregarine 

 Monocystis however we find a particularly beautiful example 

 (Figure 46). In the flagellates, Schaudinn (1904) and 

 Prowazek (1904) described a reduction from 8 chromosomes 

 to 4, in a number of species (Trypanosoma noctuae, T. 

 lewisi, T. brucei, and Herpetomonas). The accuracy of 

 these accounts has been called in question. 



Bott (1907) has described the reduction of the number of 

 chromosomes in the rhizopod Pelomyxa, an animal re- 



Figure 50. Reduction of the number of chromosomes before mating 

 in the rhizopod Pelomyxa, after Bott, 1907. A, the eight oval chromo- 

 somes of the parent. B, first of the two maturation divisions; the 8 

 chromosomes separating into two groups of 4. C, the second matura- 

 tion division; in the spindle to the left each of the 4> chromosomes (of 

 which but 3 are in view) is dividing into two. 



sembling a large amoeba. The single animal contains many 

 nuclei. At times these go through two divisions in succes- 

 sion, which may be called the maturation divisions (see 

 Figure 50). At first there are eight oval chromosomes 

 (A). At the first division (B), four of these go into one 

 of the resulting cells, four into the other; the number is 

 thus reduced. At the second division each of the four 

 chromosomes is divided (C), so that all the nuclei produced 

 have four chromosomes. Later each of these nuclei, along 

 with a little cytoplasm, separates from the body of the 



