191f>.| NATURAL SCIENCES OF PHILADELPHIA. 21 



the parasite lias wholly disappeared and the vacuole in which the 

 nucleus lies is the vacuole originally formed by the parasite. 



Fig. 33, Plate II. represents a parasite from the same slide and same 

 section of the intestine as figs. 31 and32. It is clearly a female. The 



entire parasite is sharply outlined, and the cytoplasm is dense, 

 although showing several vacuole-. The nucleus is clear cut and 

 contains a large, rather faintly staining karyosome, together with 

 two black granules. * me of these granules lies within the karyosome. 

 the other appears to be in the space between the karyosome and 

 membrane, but it is possible that it actually lay upon the membrane 

 itself. In this particular case, strands connecting the karyosome 

 with the nuclear membrane could not be detected. 



Fig. 34 was also obtained from the same slide as figs. 31, 32, and 

 33, but not from the same section. The parasite was clearly outlined. 

 The cytoplasm, while not suggesting degeneration, was not homo- 

 geneous, but appeared to consist of a matrix in which were a number 

 of poorly defined denser areas. This is an appearance frequently 

 to be noted in the early female stages, but it has not been possible 

 to work out its significance. The nucleus of this parasite was clear 

 cut and contained a large, faintly staining karyosome. Little 

 strands radiated from the karyosome, but these could not be traced 

 to the nuclear membrane. Two black granules were present, one 

 within or upon the karyosome, the other on the nuclear membrane. 



The four parasites here figured and described typify conditions as 

 found in mouse 250. They appear to furnish satisfactory evidence 

 that the spores, after their invasion of the cells, separate into two 

 groups, the later evolution of which indicates that they are to be 

 regarded as males and females. This evolution, moreover, proceeds 

 at such a rate that at the end of five hours at least a considerable 

 number of the parasites can be separated into males and females. 

 It is also believed that the cases herewith considered are the more 

 convincing in that they were all taken from exactly the same place 

 in the intestine. This was the twenty-second piece of an intestine 

 cut into 34 pieces and therefore only two-thirds the way from the 

 anterior end. This permits of the presumption that these four 

 parasites had all entered the cells at somewhat the same time, and 

 that this was perhaps four hours prior to the death of the mouse. 



It is of course to be understood that in the whole intestine up to 

 6 hours, and in its extreme posterior portions up to 9 hours, the 

 parasites are in general in all sorts of conditions and that only a 

 portion are differentiated into males and females. Furthermore, 



