212 BIOLOGICAL LECTURES. 



some complex, some remarkably simple, that it is possible to 

 pick out a series which represents the stages through which 

 the complicated mitotic figures of the higher plant and animal 

 nuclei may have passed in their evolution to the present 

 state. It must be distinctly understood, however, at the out- 

 set, that these variations among the Protozoa give absolutely 

 no clue to the phylogeny of the Metazoa and the Metaphyta ; 

 all that they show, at the most, is that the various forms here 

 considered have arrived at a certain grade of differentiation 

 where they have stopped, although it may be logically inferred 

 that similar stages have been passed through by the higher 



forms. 



Beginning with the division which most closely resembles 

 mitosis for the first type as described above, we shall see that 

 the process in the cystoflagellate Noctihica can be described 

 in almost the same terms as that of the Metazoa.^ The nucleus 

 is of large size, with a distinct membrane, and with chromatin 

 in the form of large reservoirs {Bitinenkoifer of Rhumbler, 

 Chromatosphere of Doflein) from eight to eleven in number. 

 The remainder of the nucleus is filled with large granules, 

 which have a distinct affinity for the acid dyes. There is no 

 trace of linin network or " achromatin " other than the large 

 granules, which may be identical with Reinke's oedematin 

 granules. Upon the outside of the nucleus, in the cytoplasm 

 and close against the nuclear membrane, is a large, faintly 

 staining mass, which corresponds with the sphere in higher 

 cells, and which during division acts as a kinetic center. 



During the early stages of mitosis the chromatin reservoirs 

 break down, by repeated division, into an immense number of 

 minute chromatin granules, which, at first collected in groups 

 in the region of the reservoirs from which they were severally 

 derived, later become distributed about the nucleus until the 

 latter is apparently filled with them. The granules are then 

 collected again in lines which radiate inwards from the nuclear 

 membrane at the point where the sphere is in contact (Fig. 

 \, A)\ these lines form the chromosomes, which soon become 

 double. The chromosomes thus formed are later connected 



1 Cf. Calkins, Mitosis in Noctiluca miliaris. Boston, Ginn & Company, 1898. 



