1916.] NATURAL SCIENCES OF PHILADELPHIA. 29 



section, whereas in the other two figures more than an optical section 

 is shown. Figs. 75 and 7ti are the more typical; in fig. 71 the para- 

 site is unusually small for this stage, but is characteristic in showing 

 very clearly the arrangement of the microgametes around the 

 periphery. 



The fully evolved male element or microgametocyte is a rounded 

 or oval body, showing a stringy or amorphous residual mass and a 

 -tries of microgametes disposed around the periphery. These latter 

 are bodies about 2 to 2.5 microns long, broader at one end than the 

 other and apparently composed wholly of intensely basophil chro- 

 matin. This is at least their appearance in sectioned material, it 

 is not impossible that in life, or in material otherwise prepared, 

 they may show more than is here evident. Analogy would lead us 

 to suspect the existence of flagella. 



This stage is apparently of short duration. Mouse 152, killed 

 18 hours after feeding, was heavily parasitized, but the exact stage 

 shown in fig. 75 was comparatively scarce. This, however, is much 

 as might be expected. The presumption is that the microgametes 

 are motile elements, and once they 'are fully ripe they doubtless 

 quickly abandon the situation in which they evolved, and without 

 them the residuum would scarcely be recognizable. 



In number they varj-, following the counts made, from 13 to 17. 

 Allowing both for an actual- variation and for the practical difficulties 

 in making an accurate determination, the supposition is plausible 

 that the typical number is sixteen. It is a familiar biological 

 phenomenon that in those cases where the number of elements 

 ultimately produced is some power of two, we are dealing with the 

 results of the repeated division of some one original element. In 

 this case, however, the end appears to lie attained in a less regular 

 manner. 



In the description of the later stages of the e\ r olution of the male 

 element, reference was confined to the conditions as found in mice 

 106, 120, 152, and 179, respectively, 9, 10| and 17, 18 and 16| hour-. 

 The first three of these gave particularly favorable material, all of them 

 being heavily parasitized and none showing much destruction of 

 the cells. The conditions seen here, however, were duplicated in 

 other mice. Thus, Nos. 113, 132, and 133, all either Sh- or 9-hour 

 periods, showed many of the same stages as were seen in mouse 106, 

 while the later stages in the evolution of the microgametes were seen 

 in mice 121, 175, 177, 178, 180, and 182, representing periods ranging 

 from 10| to 18 hours. 



