276 PROCEEDINGS OF THE ACADEMY OF [June, 



decrease in size (fig. 15) and eventually they too disappear. The 

 mature spore (fig. 16) is about 3 microns long and 1.5 microns wide; 

 the ends are oval and a slight constriction is usually found in the 

 middle region. In a single section of a cell of Bidder's organ one may 

 find as many as 15 cysts, containing spores in practically all stages of 

 development, from that shown in fig. 7, a, to that of the mature spore 

 shown in fig. 16. As cysts containing spores that stain very faintly may 

 lie adjacent to cysts in which the spores are all stained black, it is 

 evident that the great affinity of the cytoplasm for the iron-hsema- 

 toxylin is not due to an overstaining of the material, but to some 

 change taking place in the substance of the spore itself. 



As the more intense staining of the cytoplasm of the spore is invari- 

 ably coincident with the disappearance of the nuclei from the vacuoles, 

 it would seem as if the two phenomena must be related in some way ; 

 and it is possible that, after the stage of fig. 1 1 , the chromatin substance 

 gradually becomes distributed throughout the cytoplasm and brings 

 about a deeper staining of the spore contents. Although I have found 

 a large number of spores in which the nuclei are of various sizes and 

 stain with different degrees of intensity at the outer border of the 

 vacuoles, I cannot be certain that the nuclei break down at this place; 

 for I have found several spores like those shown in figs. 24 and 25, in 

 which two nuclei lie in the cytoplasm after the vacuoles have moved to 

 the ends of the spore. I have not succeeded in finding any stages that 

 would seem to connect fig. 11 with fig. 24, yet it is possible that soon 

 after the stage of fig. 11 the nuclei pass quickly from the vacuoles 

 into the cytoplasm which at once stains more intensely. From the 

 evidence at hand, I am inclined to believe that the spores shown in figs. 

 24 and 25 are abnormal and that the nuclei gradually disintegrate at 

 the outer border of the vacuoles. 



In the second type of development, which is not as common as the 

 type just described, the nucleus moves to one end of the spore and 

 takes a position as shown in fig. 17. A vacuole then forms around the 

 nucleus as in Type I (fig. 18), and subsequently the nucleus divides 

 (fig. 19). Later the two nuclei, which stain as intensely as in the 

 earlier stages, move to opposite ends (figs. 21, 22) or, in some few cases, 

 to opposite sides (fig. 20) of the vacuole. The vacuole increases in size 

 as the spore elongates ; but, as far as I have been able to determine, it 

 does not divide into two parts, as does the vacuole in the spores that 

 follow the first type of development. After the disappearance of the 

 nuclei in the stage succeeding that of fig. 22 the vacuole gradually 

 becomes smaller (fig. 23), and the entire spore stains black and appears 

 as in fig. 16. 



