l'JIO.] NATURAL SCIENCES OF PHILADELPHIA. 13 



contained them in considerable abundance. These differences are. 

 as already suggested, probably to be accredited to differences in the 

 manner in which the two mice led. 



Taking up now the evolution of the spores within the intestine of 

 the mouse, we may advantageously use as a point of departure the 

 -pore as it occurs free in the lumen, for it is evident that development 

 lu 'gins here. 



Plate I, fig. 2, portrays such a spore and may be taken as the 

 point of departure, although in all the early stages the spores in the 

 lumen are identical with many of those in the cells. This particular 

 case is from mouse 248, a 2-hour stage, but it is valid for any of the 

 early stages. 



The characteristics of this stage are as follows: The contours of 

 the cell are sharp and clear cut, and there is a distinct bounding line 

 or periplast. The cytoplasm, while obviously alveolar, is dense and 

 ordinarily stains well. Granules may or may not be present. The 

 nucleus, which is conspicuous, is round and gives the appearance as 

 though in life it were turgid with nuclear sap. There is a distinct 

 nuclear membrane and a more or less distinct nuclear net is always 

 present. 



With regard to its shape, the spore in the lumen may be a smooth 

 oval, as, for examples, are the intracellular spores shown in Plate I, 

 figs. 3 and 4, or it may have the sides more or less bulged out in the 

 region of the nucleus. This latter phenomenon is due to the increase 

 in size of the nucleus, a process initiated very shortly after the spore 

 reaches the alimentary canal of the mouse. 



The appearance of the spores in the intestine, whether they be 

 in the lumen or in the cells, offers a considerable contrast to that of 

 spores removed from the cysts. . With regard to these latter, a 

 description is herewith given, although they are familiar objects 

 in the literature and have been described and figured a number of 

 times. 



Such spores are shown in Plate I, fig. 1. As is here indicated, one 

 end of the spore is broader, the other end narrower, and the nucleus 

 lies nearer the narrow end. 



The internal structure is obscure. The nucleus is a clear-cut 

 vesicle, and to all appearances is provided with a definitive mem- 

 brane. Xo internal structure can be made out, and the staining 

 reaction is feeble. In Giemsa preparation- it stains a pale reddish 

 color. 



The cytoplasm with Giemsa stains a dense blue. Its structure can 



