382 PROCEEDINGS OF THE ACADEMY OF [June, 



Negri may be only groups of sporoblasts, and it is in harmony with 

 this opinion that in both cases these authors figure slightly later 

 stages of the parasite in which the sporoblasts are completely 

 individualized. 



More direct evidence, however, is furnished by some material which 

 has recently been examined by the present author. This, from the 

 heart of a sheep, appears to show that at least in the case of Sar- 

 cocystis tenella, the sarcosporidian cyst originates from a single cell. 

 This conclusion is based upon the discovery of a single partly divided 

 sporoblast, lying in a minute cavity within a cell of the heart. Divi- 

 sion had progressed to the point where the two daughter cells were 

 wholly distinct, but still in intimate contact. The next stage found 

 consisted of a group of eight sporoblasts, also lying in a cavity within 

 a heart cell. All of these eight sporoblasts were more or less com- 

 pletely individualized. In addition to these very small stages, 

 larger groups of sporoblasts were found, up to cysts of over 100 p- 

 long. But in all cases the elements composing the groups were 

 obviously the same as the sporoblasts of Negri and Bertram. 



Thus the data furnished by Bertram, Negri, and the present 

 author are entirely consistent amongst themselves, and are mutually 

 confirmatory and supplementary. For although the earliest known 

 stage of S. muris yet discovered consists of a number of cells, about 

 six or seven, judging from Negri's figure, we can hardly ascribe to it 

 a mode of development different from that of S. tenella. Assuming 

 then that these data are accurate, a certain interesting conclusion 

 seems to follow. 



This conclusion is in effect 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. 



Assuming that this is true, the life history of Sarcocystis muris 

 would be as follows: The ingested spores gain the epithelium of 

 the intestine and develop into the macrogametes and microgametes. 

 The latter fertilize the former and produce the zygotes. By endo- 

 genous multiplication the zygotes produce a number of minute 

 elements. There is here a gap in the life history. It is evident 

 that two divergent lines are followed since, as we have seen, some 

 form of the parasite appears in the feces from the fifteenth to the 

 sixtieth day. It is therefore impossible to say whether the multi- 

 plication products described by Erdmann are those destined to 

 invade the muscles or to infect the feces. But whatever happens, 



