L916-] NATURAL SCIENCES OF PHILADELPHIA. 37 



evidenl increase in size. The unclear net does not develop as it does 

 in the male parasite, luii the chromatin concentrates into a single 

 large karyosome which maintains an acidophil rather than a basophil 

 staining reaction. 



(11) In the 6- to 15-hour periods, phenomena are seen which seem 

 besl interpreted by regarding them as maturation. Irregular 

 chromatin granules appear in close association with the nuclear 

 membrane. Later these granules pass out into the cytoplasm, and 

 finally disappear. 



(12) The mature female, or macrogamete, may be found in mice 

 killed from 11 to 18 hours after inoculation. 



(13) Finally, in the 18-hour stages, macrogametes may be found 

 which in some cases show minute, thread-like bodies upon their 

 surfaces, and in others contain within their substances small solid 

 chromatic bodies, one in each case. These appearances are regarded 

 as warranting the interpretation that fertilization takes place. 



Explanation of Plates I, II, III, IV, V. 



The original figures wore made by the author and later copied in ink by Mr. 

 Haines, artist of the Bureau of Animal Industry. The greater number are 

 from camera outlines, made on the table with a 2 mm. apoehromatic objective 

 and Xo. 18 eyepiece. This method yields a magnification of about 3,530 diame- 

 ters. The remaining drawings are free-hand sketches of approximately the same 

 enlargement. In reproduction, the drawings have been reduced in the ratio 

 of 3 to 2, and hence are about 2,350 times larger than the objects themselves. 



In order to show the relationships between the parasites and the cells, the 

 latter have in some cases been drawn in outline. It was not, however, considered 

 necessary to do this throughout. 



Plate I. — Fig. 1. — Camera outline. Giemsa stain. Spores taken directly from 

 a cyst. The cytoplasm stains a dense blue; the nucleus is a reddish vesicle 

 with little or no internal structure. The spores are broader at one end 

 than the other. 



Fig. 2. — Camera outline. Thionin and acid fuchsin. Mouse 248, 2 hours, 

 int. 30. Spore free in lumen. Cell outlines clear cut; a periplast present; 

 cytoplasm shows no signs of degeneracy. The nucleus shows a nuclear 

 net and is somewhat enlarged, causing the cell edges to bulge. 



Fig. 3. — Camera outline. Delafield and acid fuchsin. Mouse 251, 1§ hours, 

 int. 9. Cytoplasm slightly degenerate, but staining deeply. Nucleus 

 enlarged, about to cause bulging of the sides of the cell and showing a central 

 mass joined to the nuclear membrane with strands. 



Fig. 4. — Camera outline. Delafield and acid fuchsin. Mouse 251, 1J hours, 

 int. 9. Cytoplasm dense and staining deeply. Nucleus enlarged, with 

 the central mass separated into granules. 



Fig. 5. — Camera outline. Delafield. Mouse 248, 2 hours, int. 27. Cytoplasm 

 dense with occasional clear spaces. Nucleus not enlarged. Chromatin in 

 the form of small granules distributed throughout the net. 



Fig. 6. — Camera outline. Thionin and acid fuchsin. Mouse 248, 2 hours, 

 int. 30. Cytoplasm very solid, staining deeply with the thionin and showing 

 no signs of degeneracy. Nucleus is a vacuole which stains more or less 

 homogeneously, apparently due to the fact that the nuclear sap has stained 

 as well as the nuclear net and thus the latter is obscured. This is a frequent 

 appearance, especially in parasites free in the lumen. 



