24 PROCEEDINGS OF THE ACADEMY OF [Jan., 



when the chromatin is divided into chromosomes, and this is also 

 the time when it stains most intensely. 



In the case of Protozoa, the resting, or better the trophic, nucleus 

 takes the plasma rather than the chromatin stains, a fact which 

 may be ascribed to an extremely low content in nucleic acid at such 

 times rather than to a fundamental difference between the chemistry 

 of protozoan and metazoan nuclei. But when in division, the 

 protozoan nucleus stains as does that of the Metazoa, and this 

 same staining reaction is also displayed by certain of the products of 

 this division, such as microgametes. 



It is therefore permissible to suppose that in these early male forms 

 of Sarcocystis muris, the coarseness of the threads of the nuclear net 

 is due to the fact that the achromatic filaments are bearing a quantity 

 of chromatin poor in nucleic acid. Besides being distributed along 

 the achromatic filaments and upon the inner surface of the nuclear 

 membrane, the chromatin may also occur in lumps, in masses which 

 fill up the meshes of the net, and there is apparently normally present 

 a larger mass or karyosome. 



In the course of several hours, however, this type of nucleus trans- 

 forms itself into a body such as is shown in figs. 66 and 67 (Plate IV) . 

 This is an oval element containing some achromatic stringy substance 

 and showing around the periphery a series of granular clusters. 

 The granules composing these clusters are extremely minute, but 

 intensely chromophil, staining as do the chromosomes of a dividing 

 metazoan cell. In spite of their minute size they are readily resolved. 



We thus start with a nucleus having a considerable bulk of chro- 

 matin which has a low affinity for chromatin stains. Morpho- 

 logically, this chromatin occurs as granules, irregular masses and 

 bands, borne either by the nuclear net or upon the inner surface of 

 the nuclear membrane. There is also usually present a central mass 

 or karyosome. After several hours, however, the chromatin has 

 diminished in bulk, has an intense affinity for chromatin stains, and 

 is placed around the periphery in the form of clusters of minute 

 granules. The conspicuous changes then consist in the taking on 

 of a high affinity for basic stains, subdivision into minute granules 

 and migration to the periphery. 



The desire is to show the several steps in this transformation. 



The earlier conditions are shown by figs. 31, 32, 38, and 39. Figs. 

 31 and 32 are from mouse 250, a 5-hour stage; fig. 38 from mouse 

 253 (6 hours), and fig. 39 from mouse 99 and presumably represents 

 the 6-hour stage. These four figures show very distinctly the 



