20 PROCEEDINGS OF THE ACADEMY OF [Jan., 



further, although it is still difficult to get forms that can positively 

 be diagnosed as females. 



An evident female, however, is shown in fig. 28, Plate II. This is taken 

 to be a female on account of its shape, its retention of the cytoplasm, 

 and the character of its nucleus. This latter element, as is shown 

 by the figure, is vesicular, with a sharply defined nuclear membrane 

 and a central mass of chromatin from which strands radiate to the 

 periphery. Fig. 29 shows another female. This figure is diagram- 

 matic, but is essentially like fig. 28. Both of these figures were 

 obtained from int. 14 of the mouse; that is, from the anterior half 

 of the intestine, and hence the presumption is that both of the 

 parasites drawn had been in the cells for some considerable time. 



Fig. 30, from int. 19, may also be that of a female, although here 

 the diagnosis is more doubtful, since the form rather suggests a 

 parasite which has been in the cell for only a short time. 



In addition to the females, characteristic early males were seen 

 in the cells of this mouse. 



Mouse 250. — This mouse was killed five hours after feeding. Its 

 intestine was cut into 34 pieces, numbered from 1 to 34, and observa- 

 tions were made on int. 21, 22, and 32. 



In this mouse it is much easier to distinguish between the males 

 and females, since the two lines of development have become well 

 separated. Thus, figs. 31 and 32, Plate II, represent males which have 

 reached what might be termed the nuclear stage; that is, the stage 

 in which the cytoplasm has nearly or quite disappeared. 



Thus, in fig. 31, the cytoplasm has all disappeared except for a 

 cap of degenerate-looking material at one end of the nucleus. The 

 nucleus itself shows the usual net, associated with which are several 

 black granules. Centrally there is an irregular mass of acidophil 

 chromatin in which lies a large black granule. This probably 

 represents the karyosome. 



Fig. 32 also represents a male. There is here to be seen a well- 

 defined net of rather broad strands and a number of black granules. 

 The meshes of the net are in some places filled with faintly staining 

 material. A karyosome does not appear to be present, although the 

 large black granule may perhaps represent it. The crescent of 

 staining substance at one end of the nucleus may represent the 

 remnant of the spore cytoplasm, but more probably is a crescent of 

 host tissue which not infrequently forms at the end of the vacuole 

 in which the parasite normally lies. Its actual detachment from the 

 parasite suggests it is the latter, and if this be so the cytoplasm of 



