14 PROCEEDINGS OF THE ACADEMY OF [Jan., 



scarcely be determined, but it may be inferred that it is alveolar. 

 It is densest in the immediate vicinity of the nucleus. The broad 

 end of the spore is frequently much less dense than elsewhere and 

 at times shows a more or less well defined oval area. This appear- 

 ance, however, is probably due merely to the fact that here the 

 cytoplasm has a lower affinity for the stain than elsewhere. 



The same phenomenon is shown by the spores of Sarcocystis 

 leporum (Crawley, 1914). In the case of the rabbit parasite, as I 

 have endeavored to show, one end of the spore seems to be differen- 

 tiated into a sort of rostrum, the cytoplasm of which does not stain 

 as densely as does that of the balance of the spore. We are probably 

 dealing with the same thing in the case of Sarcocystis muris, but in 

 this parasite the differentiation of the rostrum is not so sharp. It 

 may furthermore be suggested that it is this clearer region in the 

 spore which has given rise to the belief, expressed by some authors, 

 that the sarcosporidian spore possesses a polar capsule. 



Comparing the spores taken directly from a cyst with those in the 

 intestine, the latter are broader, more oval bodies, and, although 

 this is not shown by the figures, there has been a loss of the granules 

 which are such a characteristic feature of the former. The most 

 noteworthy change, however, concerns the nucleus, which has 

 become larger, apparently much more turgid, and begins to show a 

 nuclear net. 



It is thus evident that evolution begins as soon as the spore reaches 

 the intestine of the mouse, and apparently the most important step 

 is a great increase in activity of the nucleus. This evolution, however, 

 does not appear to be carried far unless the spore gains a resting place 

 within a cell of the host. 



The cells invaded are the cylinder cells. At least this is so in the 

 vast majority of cases. Now and then, however, parasites are to be 

 found in mucous cells, but since the presence of a parasite in a cell 

 may result in mucoid degeneration, it is difficult to diagnose such 

 instances. The parasite may have invaded a mucous cell or it may 

 have caused mucoid degeneration of a cylinder cell. This question, 

 however, appears to be of no great importance. 



It is also well to emphasize the point that the spore is a naked 

 mass of protoplasm and that the only differentiation displayed by 

 the cytoplasm is the peripheral condensation into a periplastic layer. 

 Statements to the effect that the spore opens and releases an amcebula 

 are wholly without warrant, and polar filaments, either coiled up 

 within one end of the cell or discharged, do not exist. Claims of 



