12 



BULLETIX 120, UNITED STATES NATIONAL MUSEUM. 



the branching threads connecting them are superficial, lying just 

 beneath the caryotheca. The chromatin granules and the chromatin 

 threads connecting them lie somewhat more internal. Through 

 the whole nucleus lie the achromatic granules and threads or films, 

 not drawn in the figures. Perhaps the achromatic threads are really 

 films giving the appearance of threads when seen in edge view. 

 The chromatin threads appear to be true fibrillae. Near the center 

 of the nucleus lies a spheroidal plasmosome nucleolus, itself seen to 

 be vacuolated, or alveolar^ when properly stained (posterior nucleus 

 of figure 3). With some of the hematoxylin stains, Delafield's for 

 example, the nucleolus does not usually stain. Borax carmine and 

 numerous other stains, as for instance Lichtgritn^ bring it out well. 



Fig. 4. — Mito.sis i.\ Protoopamna intestinalis. X 800 diameters. The achromatic 



STRUCTURES IN THE NUCLEI ARE OMITTED. THE MICROCHROMATIN IS SHOWN ONLY IN 

 FIG. a. a, A NUCLEUS IN THE RETICULATE CONDITION, ONLY THE STRUCTURES ON THE 

 UPPER SIDE OF THE NUCLEUS ARE DRAWN ; 6, AN ANTERIOR NUCLEUS WHICH IS PASSING 

 OUT OF THE SKEIN CONDITION, THE MACROCHROMATIN BAND BEGINNING TO DIVIDE INTO 

 MACROCHROMOSOMES, ONLY THE MACROCHROMATIN BEING DRAWN ; C, A NUCLEUS IN 

 WHICH THE MACROCHROMATIN IS IN DISTINCT MASSES ; d, AN ANAPHASE NUCLEUS ; e, AN 

 EARLY METAPHASB SHOWING ONLY MACROCHROMATIN IN THE DRAWING. THE MACRO- 

 CHROMOSOMES ARE UNITED SIDE TO SIDE BY THIN PLATES OF CHROMATIN, DRAWN ONLY IN 

 OUTLINE. (This figure is schematic, the individual size and form of THE SEVERAL 

 CHROMOSOMES NOT BEING SHOWN.) f, THB APPEAR^^NCE OF SPLITTING OF THE CHROMO- 

 SOMES IN THB STAGE IMMEDIATELY FOLLOWING THAT SHOWN IN C. 



There is ho demonstrable centrosome in either the nucleus or the 

 cell body at any time, whether the nucleus be in " rest " or dividing 

 by mitosis. 



Mitosis seems to follow the same course in all the Protoopalinas 

 and Zelleriellas, and in Cepedea and O'palina the phenomena are 

 very similar, but are not so easily followed in these smaller nuclei. 

 In the reticulate nucleus there are, as described, a persistent caryo- 

 theca, superficial chromatin masses with their connecting branched 

 chromatin threads, somewhat more internal chromatin granules with 

 their branched connecting chromatin threads, and an achromatic 

 stroma consisting of slightly smaller granules and connecting films 

 or fibrillae. As the nucleus enters upon mitosis (fig. 4,(7), it elon- 

 gates parallel, or nearly parallel, to the long axis of the body, and 



