1916.] NATURAL SCIENCES OF PHILADELPHIA. 25 



variations with regard to what is interpreted to be the karyosome. 

 In fig. 32 it is either absent or represented by the large black granule. 

 In fig. 31 the irregular central mass provided with a Mack grannie 

 presumably represents this element. In fig. 38 it is a large irregular 

 body, while in fig. 39 it is a large oval deeply staining granule, splil 

 nearly into two by a cleft. To some extent these differences are 

 due to the technique employed, but in the main they represent actual 

 differences in the morphology of the parasite itself. 



Passing now to mouse 106, a 9-hour stage which yielded highly fav< >r- 

 able material, we have figs. 40and41 (Plate III). Fig. 41 is very much 

 like fig. 39, except for the staining reaction of the karyosome. Fig. 

 40 bears a general resemblance to figs. 31, 32, and 38. It is therefore 

 apparent that figs. 40 and 41 represent the earlier of the stages 

 present in mouse 106 and hence the starting point from which a 

 number of these have arisen. For the parasites in a 9-hour mouse 

 may have been in the cells anywhere from a very short time up to 

 perhaps 8 hours. Hence, in passing from mouse 99, 250, or 253 to 

 mouse 106, it is not necessary and would, indeed, be a mistake to 

 assume that we had also passed over 3 or 4 hours of time spent in 

 development. The period elapsing between the inoculation and 

 death of the mouse, at least as far as concerns the periods up to 9 or 

 10 hours, is of value only as a high limit. A parasite of mouse 253 

 cannot be more than 6 hours old; one of mouse 106 cannot be more 

 than 9 hours, and this is all that can be stated with absolute cer- 

 tainty. Nevertheless, the parasites of mouse 106 will in general be 

 older than those of mouse 253, even though they will in a number of 

 cases represent the same stages of development. It is therefore 

 permissible to use parasites such as are shown in figs. 31, 32, 38, and 

 39, as well as figs. 40 and 41, in tracing the later stages as found in 

 mouse 106. 



It is easy to pick out conditions readily derivable from these. 

 Thus, fig. 42 (upper cell) is a good deal like fig. 41. Fig. 43 is also 

 very much like fig. 41, except for the strip of basophil chromatin 

 which runs across the nucleus. Fig. 44 also displays a general 

 resemblance to the earlier stages, but has developed a greater quan- 

 tity of basophil chromatin present in the form of scattered granules. 

 A similar state of affairs is seen in fig. 45, in which the somewhat 

 quadrangular mass of acidophil chromatin situated in the centre 

 may represent the karyosome. In figs. 46 and 47, we have parasites 

 in which the chromatin is all basophil and occurs in a rather finely 

 divided state. In the case of the two parasites shown in fig. 42. 



