THK OPALIXIl) ("IIJATK IXI rSMRI AXS. 249 



ilironiatin in the form usually of larae. Hat masses lyino- just l)eneatli 

 the nuclear membrane, the reproductive chromatin in the form of 

 much smaller spheroidal ofranules. 



8. In the binucleated jrenera, Protooixil'mn. and ZeUeriHla, both 

 sorts of chromatin are, during mitosis, in the form of definite chro- 

 mosomes, the macrochromosomes (metabolic) bein«r ribbon-shaped, 

 and the microchromosomes (reproductive) l)ein<r linear airuiv^ates 

 of granules. 



4. In some species, perhaps in all. the number of uiacrochromo- 

 somes equals the number of microchromosomes. 



5. There are, in some species at least, constant differences of form 

 and size between the macrochromosomes. allowing us to recognize 

 individuality in these chromosomes. Similarly the microchromo- 

 somes differ among themselves in the number of granules they con- 

 tain, some being long strings of numerous granules, others being 

 very much shorter and having many fewer granules, others, still, 

 being intermediate. The constancy of these individual micro- 

 chromosome characters has not yet been determined by comj)arison 

 of different nuclei. 



0. There are no centrosomes in the nuclei or in the cytoplasm, in 

 the Opalinidae. 



7. The mitotic spindle fibers are of three ( ?) sorts: a. Chromatic 

 threads which are. as it were, filose pseudopodia from the macro- 

 chromosomes. During the gi-anulated condition of the nuclei these 

 chromatin fibers branch and form a coarse reticulum. The macro- 

 chromosome fibers and their branches are periplioral. just ])oneath 

 the nuclear membrane. Each macrochromosome is attached at each 

 end by such a chromatin fiber, more or less branched according to the 

 stage of mitosis, to the corresponding pole of the nuclear membrane. 

 Probably these macrochromosome fibers have a linin core. The 

 macrochromosomes themselves api)arently do have, h. Chromatin 

 threads, of similar size, lying a little more centrally, which connect 

 each end of each microchromosome with the corresjjonding pole of 

 the nuclear membrane. The condition of these microchromosome 

 fibers has not yet been thoroughly studied throughout the whole 

 mitotic cycle, c, The achromatic portion of the mitotic spindle, lying 

 in the axis of the nucleus, seems somewhat fibrillar, but the ai)parent 

 delicate fibrillae may be but emphasized longitudinal films of the 

 achromatic alveolar substance. 



S. The fact that each chromosome is bound by each end to the cor- 

 responding pole of the nuclear membrane, and that the connection is 

 not lost even in the reticulate ]:>liase of the mitotic cycle, makes these 

 nuclei particularly favorable for the study of certain cytological 

 pr()l)lems. 



83103—23 17 



