350 H. S. DAVIS 



zoites for I have never seen anything to indicate that they 

 may develop into the smaller disporous type. During the 

 months of June, July and August, when these observations were 

 made, the formation of gemmules is certainly the principal 

 method of reproduction in the case of the polysporous tropho- 

 zoites, for sporulating individuals were always rare, and in 

 many fish none at all were found, while trophozoites containing 

 gemmules were always abundant. Whether this be true at other 

 times of the year I am unable to say. 



The spores are developed from generative cells similar to those 

 which form the gemmules. Unlike the disporous form, the spores 

 always develop in pairs from a common pansporoblast, the sporo- 

 blasts of which are never separated. Each pansporoblast origi- 

 nates from a single cell, but in this case the entire cell divides, 

 so that the developing pansporoblast can be easily distinguished 

 from the gemmules, in which only the nuclei divide. During 

 the multiplication stage the generative cells separate soon after 

 division, but in the pansporoblasts the daughter cells remain 

 closely associated (figs. 76 and 77) although the outlines of the 

 individual cells can usually be easily distinguished. Unlike the 

 sporoblasts of the disporous form, the cytoplasm of the pan- 

 sporoblasts does not ordinarily stain more deeply than the sur- 

 rounding endoplasm. However, in a few cases I have noticed 

 pansporoblasts in which the cytoplasm was denser and stained 

 more intensely, while the outlines of the individual cells were 

 indistinct and difficult to make out (fig. 79). Such pansporo- 

 blasts appear strikingly like the sporoblasts of the disporous 

 trophozoites except that the nuclei never contain a nucleolus. 



The cells in the pansporoblasts do not have any such definite 

 arrangement as in the sporoblasts of the disporous form, and it is, 

 therefore, impossible to trace the derivation of the different cells 

 of the spores, but there is no reason to think that it is essentially 

 different. The fully developed pansporoblast contains twelve 

 cells as in figure 78, in which eleven cells occurred in the section ; 

 the other cell which was in the next section is not shown. A care- 

 ful study of a number of pansporoblasts which were sufficiently 

 separated from adjoining cells to admit of an accurate count 



