2l8 J. MCA. KATER. 



many living ones watched continuously during the process of 

 excystment without the slightest evidence of propagation. There 

 is no indication of a sexual phase in any part of the life cycle. 



Mitosis. By far the greater number of flagellates in which 

 mitosis has been studied possess within the nucleus an endosome 

 and, surrounding this body, scattered chromatin granules. It is 

 from this scattered material that the chromosomes are usually 

 formed. In Polytomella citri we have a different story, all of the 

 chromatin being located in a single central body, the karyosome * 

 (Parapolytoma satura has a very similar nucleus, Jameson, 1916). 



The orderly behavior of the karyosome during the early part of 

 the prophase is very interesting. The first indication of mitosis 

 is the bisection of this body in a plane transverse to the long axis 

 of the cell-body. The two parts appear to be equal and they pull 

 slightly apart, leaving between them a light cloud. A second 

 division follows the first and forms at right angles with it. The 

 karyosome now consists of four parts which still have the chro- 

 matic cloud between them. In the next stage that could be found 

 eight karyosomal bodies, imbedded in the chromatic cloud, were 

 visible. Since the karyosome is spherical we would expect a 

 division, corresponding to the third cleavage of a fertilized egg, 

 between the last two. It may be that such is the case, but the 

 minute size of the objects made it impossible to determine. The 

 division of the karyosome continues until more than twenty 

 particles can be made out, still imbedded in the chromatic cloud. 

 It is interesting to note that the anchoring strands are still per- 

 sisting. Careful observations were made in an attempt to de- 

 termine whether they connected, internally, with individual 

 granules or were a part of some achromatic supporting structure 

 within the karyosome, but without results. 



In the next step the chromidial cloud lightens, the nucleus 

 becomes transversely elongate to a slight extent, there is a conden- 

 sation of the numerous small granules and a spireme appears. 

 This consists of seventeen or eighteen chromatin bodies connected 

 by slender achromatic strands. When the nucleus lengthens 



1 There is no question concerning the nature of the chromatic body within the 

 nucleus of Polytomella and since karyosome has a more restricted meaning than 

 endosome it can well be used here, though I consider that endosome, as suggested 

 by Minchin, is a valuable term for the nucleoli of many protozoan nuclei. 



