476 SUMMARY OF CUERENT RESEARCHES RELATING TO 



becomes evident. The granules characteristic of the spore as it occurs 

 in the cyst either disappear or become much less evident. The spores 

 are sexually differentiated, but it does not appear to be possible, at the 

 outset, to distinguish between the males and the females. 



Within the cells of the mouse, the changes undergone by the male 

 spores, or microgametocytes', began to be evident in one and a half to 

 two hours. The size of the nucleus increases further ; the nuclear net 

 is further developed ; the cytoplasm degenerates and disappears in about 

 six hours. The microgametocyte is reduced to its original nucleus, 

 which, however, is of approximately the same size as the original spore. 

 The reduction of the cytoplasm is a very remarkable phenomenon. 



Three internal changes go on more or less simultaneously. The 

 chromatin appears to suffer a loss in actual bulk, and alters in staining 

 reaction from acidophil to basophil. The chromatin, which occurred in 

 large irregular masses or distributed along the threads of the linin net in 

 strips or bands, is reduced to granules which become smaller and smaller 

 and show a greater and greater affinity for chromatin stains. These 

 granules finally assemble in clusters around the periphery. 



The next step is the solidification of these granular clusters into 

 rounded solid balls. These elongate into minute thread-like bodies, 

 the microgametes. These are found at their acme in mice killed eighteen 

 hours after inoculation. 



The females go through their development side by 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. In the 

 course of a few hours, however, the females can be picked out, appear- 

 ing 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 evident increase in size. The nuclear net 

 does not develop as it does in the male parasite, but the chromatin con- 

 centrates into a single large karyosome, which maintains an acidophil 

 rather than a basophil staining reaction. 



In the six to fifteen-hour period phenomena occur which may be 

 regarded as maturation. Irregular chromatin granules appear in close 

 association with the nuclear membrane. These granules subsequently 

 pass out into the cytoplasm, and finally disappear. 



The mature female, or macrogamete, may be found in mice killed 

 from eleven to eighteen hours after inoculation. Fiually, in the 

 eighteen-hour stages, macrogametes may be found which in some cases 

 show minute, thread-like bodies upon their surface, and in others contain 

 within their substance small solid chromatic bodies, one in each case. 

 Fertilization has occurred. 



Zoological Position of Sarcosporidia.* — Howard Crawley discusses 

 the idea that the muscle stage of Sarcocystis muris is not an individual 

 but a congeries or colony of individuals. In other words, the unit is 

 not the cyst or Miescher's tube, but the sporoblast itself. 



* Proc. Acad. Nat. Soi. Philadelphia, Ixviii. (1917) pp. 379-88. 



