1916.] NATURAL SCIENCES OF PHILADELPHIA. 383 



it is evident that at the end of several weeks some form of the parasite 

 invades the muscles. This is either the sporobhist itself or 

 immediate forerunner, which may be the zygote or some elemenl 

 derived from the zygote. 



In any event, at a certain point in the evolutionary history, the 

 muscle cells come to harbor individual sporoblasts. These divide 

 many times by bi-partition, but eventually the products of these 

 divisions are no longer sporoblasts, but spores. It may incidentally 

 be noted that unless its development be interfered with, each sporo- 

 blast will presumably produce a cyst. 



It will be of interest to compare the several stages of the life 

 history of Sarcocystis muris with those of an ideal member of the 

 Coccidiomorpha. 



The sarcosporidian "spore" develops directly into the sexual 

 stages, the macrogametes and microgametes. These copulate and 

 produce the zygotes. In the coccidiomorphan, the merozoites pro- 

 duced at the end of schizogony follow an identical line of development. 



The sarcosporidian zygote divides into a number of small bodies, 

 the further history of which is unknown. The coccidian zygote 

 ultimately produces the sporozoites, although the details whereby 

 this end is gained are subject to great variation. 



In the sarcosporidian, some product of the zygote ultimately finds 

 its way into the muscle cells, and produces the colony of sporoblasts. 

 In the Coccidiomorpha, the sporozoites eventually find their way 

 into their appropriate habitats, which are always cells, and grow 

 into trophozoites. 



In the sarcosporidian, the sporoblasts divide a number of times by 

 bi-partition, after which spores are produced and division cease-. 

 These spores, in order to develop further, must gain the alimentary 

 canal of another host in which they will evolve into the sexual stages. 

 In the Coccidiomorpha, the trophozoites divide into merozoites 

 These grow into trophozoites, which again divide into merozoite- 

 and so on for an indefinite number of generations. Eventually, 

 however, the merozoites develop, not into trophozoites, but into the 

 sexual forms. 



It will next be in order to see what conclusions may be drawn 

 from the data given above. In so doing, it will be convenient to 

 divide the sarcosporidian life history into three portions, namely, 

 the sexual development which takes place in the intestinal .'pithelium; 

 the stage which follows this; and finally the stage which occurs in 

 the muscles. 



