204 CORA J. BECKWITH 



spheres. These are differentatied rather suddenly about the 

 time that the staining reaction of the simple yolk begins to change 

 (fig. 13). The Benda stain shows one or several small globules 

 staining with crystal-violet, within a large compound yolk-sphere, 

 the ground-substance of which is yellow brown (figs. 14, 15). 

 The size of these spheres varies considerably, some of them form- 

 ing the largest elements in the egg. The globules are arranged 

 symmetrically, and increase in size until, in the mature egg, they 

 may merge and practically fill the sphere. Usually a notched 

 edge indicates such an origin (fig. 15). Certain stains always 

 differentiate the compound from the simple yolk. Thus, saffranin 

 followed by methyl-violet gives the inner globules a bright red 

 color and the external ground-substance a pale violet color. Some 

 of the spheres never reach this state of development but appear in 

 the mature egg with small distinct globules within. It seems 

 probable from staining reactions that certain of the simple yolk- 

 spheres are utilized for the storing of a different material in the 

 form of globules. 



c. The appearance of the mitochondria. The mitochondria are not 

 seen in the egg until after the yolk is well formed, but before the 

 staining reaction of the latter has changed. As is usual for mito- 

 chondria, special fixatives (Meves' fluid, Flemming's fluid, Bens- 

 ley's fluid, formalin, hot water) are essential. When Benda's 

 staining method is used after fixation with Meves' killing fluid, a few 

 small rounded bodies, violet in color, appear here and there among 

 the yellow spheres, uniformly distributed throughout the egg (fig. 

 12). These are larger than the pseudochromatin-granules, about 

 the size of some of the smaller yolk-spheres, and of uniform size. 

 They are comparatively few at first, but gradually increase in num- 

 ber and size until they are so numerous in the mature egg that they 

 fill all the spaces between the yolk-spheres. From their first appear- 

 ance they take the typical mitochondrial stains, that is, violet in 

 Benda's stain; intense red in Bensley's stain; and deep black in 

 iron-hematoxylin. Since the question of the origin of the mito- 

 chondria has been variously answered, it is of interest to determine 

 that point in Hydractinia. As they are scattered throughout the 



