226 J. MCA. KATER. 



accepting the Polyblepharididae as the group which gave rise to 

 the sexual phenomena which are so well developed in the two 

 higher families of the Phytomonadina. 



Mitosis. The nucleus of most flagellates contains, in addition 

 to the endosome, scattered chromatin granules which seem to be 

 suspended on a linin net-work. The role of the endosome in 

 nuclear division is generally one of two types. The first, typified 

 by the Euglenoids, is the case where this body is drawn out into a 

 dumbbell shape, in the interior of the spindle, with the two knobs 

 forming polar caps. With the progress of the chromosomes to 

 the poles this structure is severed at the equator and forms the 

 endosomes of the daughter nuclei. Some writers (Belar, 1916^4, 

 Berliner, 1909, Schussler, 1917) have termed this central body of 

 the Euglenoid a "centrocaryosome," assigning to it the function 

 of a centrosome. Hall, however, has questioned this view. 

 Another type of behavior is illustrated by the endosome of 

 Polytoma (Entz, 1918) and Chlorogoninm (Hartmann, 1916) which 

 disappears during the prophase. Aragao described the formation 

 of two sets of chromosomes in Polytomella agilis, one from the 

 scattered chromatin, the other from the endosome. Doflein 

 (1916), repeating his work, found that the endosome disappeared 

 during the prophase without contributing to the formation of the 

 chromosomes. 



It is very evident that a comparison cannot be made of the 

 mitotic phenomena of P. citri and those of any form just men- 

 tioned, not even the other species of its own genus. However, a 

 similar form is found in Parapolytoma satura (Jameson, 1914) 

 which has all of the chromatin gathered into a single body, the 

 karyosome, which is suspended from the nuclear membrane in 

 much the same way as in P. citri. Unfortunately Jameson's 

 account begins rather late in the prophase, his first figure showing 

 the karyosome broken into a number of bodies which are con- 

 nected by linin strands. He states that the greatest number of 

 these ever found is sixteen or eighteen, which fuse in two's or 

 three's to form the eight definitive chromosomes. The same 

 behavior has been found in P. citri, with the addition of the early 

 stages in the fragmentation of the karyosome. Although the 

 chromosomes of P. agilis are formed from scattered chromatin the 



