36 PROCEEDINGS OF THE ACADEMY OF [Jan., 



(4) The spores are sexually differentiated, but it does not appear 

 to be possible, at the outset, to distinguish between the males and 

 females. 



(5) Within the mouse cells the changes undergone by the males, 

 or microgametocytes, begin to be evident at the end of H to 2 hours. 



(6) These changes are, first, a further increase in the size of the 

 nucleus accompanied by a further development of the nuclear net, 

 and, second, degeneration and ultimate disappearance of the cyto- 

 plasm. The cell contours become rough and irregular, vacuolization 

 occurs, the cytoplasm becomes reduced to two masses of debris 

 lying at the ends of the nucleus. These finally disappear, the entire 

 process usually being completed at the end of 6 hours. The micro- 

 gametocyte is thus reduced to its original nucleus, which, however, 

 is of approximately the same size as the original spore. 



(7) Conspicuous internal changes next take place, which modify 

 both the morphology and chemistry of the parasite. They may be 

 considered under three headings, but they all take place more or less 

 simultaneously. 



(a) The chromatin appears to suffer a loss in actual bulk, but 

 alters in staining reaction from acidophil to basophil. 



(b) From occurring in large irregular masses or distributed along 

 the threads of the linin net in strips or bands, the chromatin is 

 reduced to granules which become progressively smaller and smaller 

 and at the same time display a greater and greater affinity for chro- 

 matin stains. 



(c) These granules finally assemble in clusters around the periphery 

 of the organism. 



(8) The next step is the solidification of these granular clusters 

 into rounded, solid balls. These balls next elongate and become 

 minute, thread-like bodies, which are the microgametes. This stage 

 may be found in mice killed from 9 to 18 hours after inoculation. 

 It is very rare in the shorter of these two periods, but has apparently 

 passed its acme at the end of 18 hours. 



(9) The females go through with their development side bj r side 

 with the males, but there are no such conspicuous changes and the 

 early female stages are much like the spore which has just entered 

 the cell. 



(10) In the course of a few hours, however, the females can be 

 picked out, appearing as broadly oval cells, relatively shorter and 

 broader than the original spores. The cytoplasm is all retained and 

 assumes a rather dense alveolar texture. The nucleus shows no 



