1916.] NATURAL SCIENCES OF PHILADELPHIA. 31 



The appearances suggest maturation, a suggestion which is 

 strengthened by what is seen in figs. 84 to 87. In these the nucleus 

 is the typical vesicle with its central karyosome, while the cytoplasm 

 is more or less liberally provided with sharply staining granules. 

 It seems permissible to suppose that we are here dealing with later 

 stages in which the rejected chromatin has passed out into the cyto- 

 plasm. 



Here it is apparently absorbed, since the fully mature macrogamete 

 shows no indications of it. This phase of the life history of S. muris 

 is protrayed by figs. 88 to 91, from mice 120, 145, and 152. The 

 second of these was killed 11 \ hours after inoculation, and hence the 

 macrogamete may reach the end of its development within this 

 period of time. 



Fertilization. 



The earlier stages of the parasite are passed while within a cylinder 

 cell of the intestinal epithelium in its proper place in the epithelial 

 row. The parasite, however, has a deleterious influence on the cell 

 it invades and apparently always destroys it in the end. It would 

 then necessarily follow that the remnant of the cell, with its con- 

 tained parasite, would, by pressure, be thrust out of its place in the 

 epithelial row. In so far as the mechanics of the process are con- 

 cerned, there does not seem to be any choice as to whether the dead 

 cell would be pushed out into the lumen or beneath the row into the 

 subepithelial tissue. It looks as though one contingency would be 

 as likely to occur as the other. 



Nevertheless, as early as 9 hours, but more particularly later, a 

 considerable number of the parasites are to be found beneath the 

 epithelium. This is more particularly the case with the macro- 

 gametes, which is further in accord with the probabilities. For the 

 macrogametocyte is a rather compact, solid-looking element and 

 presumably will retain its integrity even though subjected to mechani- 

 cal stress. On the contrary, the microgametocyte, the bulk of which 

 is obviously merely decadent residual matter, would presumably 

 readily yield and break tip if acted upon by pressure. 



Here and there in the epithelium a ripe male cell occurs in which 

 the microgametes appear to be streaming out into the subepithelial 

 tissue. Conditions such as these may, of course, be interpreted in 

 two ways: the microgametes may have reached their places 

 beneath the epithelium either actively or passively. An examination 

 of fixed material clearly sheds no light on such a question, but anal- 



