16 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



by a definite clear-cut outline, which has almost the appearance of a mem- 

 brane, although no membrane has been demonstrated, nor, indeed, do I 

 believe one exists. The chromatin is aggregated into several irregular 

 dense masses, and in optical section apparently occupies about three 

 fourths of the area. Surrounding this irregular mass of chromatin is a 

 homogeneous or very finely granular substance. I do not believe that 

 this is a normal condition of the karyosphere, but I think it is the re- 

 sult of changes brought about by the massing together of the chro- 

 matin threads under the action of the fixing reagents. The spireme 

 threads, always very close together during this stage, are forced still 

 closer by the shrinking action of the fixative, thus leaving spaces which 

 are occupied only by the karyolymph. In thick sections as usually 

 stained, the minute spaces between the chromatin fibres become filled 

 with the iron-haematoxylin and cannot be decolorized ; thus the whole 

 body appears to be homogeneous, as seen in Figure 19, a. In the thinner 

 sections and in those which pass through one side of the karyosphere, 

 decolorization proceeds normally, and the result is that the individual 

 chromatin fibres are often visible, as in Figm - es 19, c, d, e. Sections 

 through one side of the karyosphere are often met with, and are very in- 

 structive in showing the true character of this body. Figures 19, e, and 

 22 represent such sections. In the former there is a denser mass of 

 chromatin (probably the accessory chromosome) upon one side, while the 

 remainder of the structure is made up of numerous granular segments in 

 cross section. In Figure 19, c?, a thin section through the centre of a 

 karyosphere at the same stage, is shown a mass or network of threads, 

 which are at some places closely aggregated, while at others they are 

 more loosely arranged, showing the individual fibres and the karyolymph 

 spaces between. Figure 19, e, is a section through a karyosphere in the 

 very early prophase, at about the stage represented in Figures 20, 21. 

 The accessory chromosome is seen at one side, while the fibres have be- 

 ■corne considerably loosened, showing more plainly the reticular structure 

 ■of the body. 



Thus we see that the karyosphere at this stage contains most of 

 ithe elements and possesses most of the characteristics of a nucleus. 

 It contains all the chromatin of the cell in the form of a spireme or 

 spiremes. This chromatin is arranged upon a linin framework, as in 

 the ordinary nucleus, and the spaces between the different strands are 

 filled with karyolymph. The only element lacking is the nuclear mem- 

 brane. Now, it is well known, from the researches of Calkins and 

 numerous other writers upon the cytology of the Protozoa, that many 



