1916.] NATURAL SCIENCES OF PHILADELPHIA. 379 



THE ZOOLOGICAL POSITION OF THE SARCOSPORIDIA. 

 BY HOWARD CRAWLEY. 



In a paper recently published by* the present author (Crawley, 

 1916), evidence was given to show that the spores of Sarcocystis muris 

 are sexually differentiated. This evidence was based upon the 

 findings in the intestinal cells of mice to which the spores had been 

 fed. It is, however, quite possible that a careful study of accurately 

 fixed and stained spores taken directly from the cysts would reveal 

 characters serving to differentiate the males and females. Certain 

 authors, for instance Fantham (1913), in the case of Sarcocystis colli, 

 speak of two kinds of spores, but nothing of the sort has as yet been 

 demonstrated in the case of Sarcocystis muris. 



Nevertheless, as already stated, these spores are males and females 

 and within the intestinal cells of the mouse they quickly develop 

 along their respective lines. This evolution is completed in from 

 9 to 18 hours, after which fertilization takes place. 



My own studies shed no light upon later events. The fertilized 

 female or zygote can be found, sometimes within the epithelial cells, 

 sometimes in the subepithelial tissues, in mice killed one or two days 

 after inoculation. But as yet I have not been able to find the 

 parasite in mice killed at longer intervals than this after feeding. 



Erdmann (1914) describes and figures what are apparently the 

 multiplication stages of a parasitic protozoan in the intestinal cells 

 and tissues of mice killed some days after the ingestion of sarcos- 

 poridian spores. The precautions taken by Erdmann seem absolutely 

 to preclude infections with any other protozoan. Consequently, 

 as the case now stands, it seems entirely reasonable to look upon these 

 multiplication stages as derived from the zygotes. 



According to Negre (1907) the feces of mice that have been inocu- 

 lated by feeding the usual cysts contain a stage of the parasite 

 capable of producing the infection if fed to other mice. This is 

 present in the feces from the fifteenth to the sixtieth day alter inocula- 

 tion. It is evidently a resistant encysted stage, since it maintains 

 its vitality for 30 days in the dried feces, and is capable of resisting 

 a considerable degree of heat. When mice are inoculated with this 

 stage, both the time required for the parasites to appear in the 

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