328 HARRY H. CHARLTON. 



vitality and a close approximation of the normal condition. 

 In such an egg the process of atresia would naturally be some- 

 what delayed. The egg with but one or two nuclei does not 

 fragment immediately, and it is possible that such eggs may 

 pass from the body, as suggested by Hartman ('16) for the 

 unfertilized egg of the opossum. This possibility is well illus- 

 trated in Fig. 1 8, which shows an unfertilized egg one hundred 

 and five hours after finding the litter. Only two nuclei are 

 present^. The mitochondrial bodies (b) can be distinguished 

 from the nuclei by their peculiar crystalline appearance and 

 elliptical shape. Although these bodies are found in most of 

 the fragmented segments to be described later, they are smaller 

 and stain less intensely in haematoxylin. They are surrounded 

 by a light area which gives them the appearance of having 

 shrunken from the cytoplasm. In Fig. 19 the mitochondrial 

 bodies are seen to be smaller but more numerous. In the two 

 upper fragments they did not cut cleanly but were pushed aside 

 by the knife. This would seem to indicate that they were much 

 more compact and dense than the surrounding cytoplasm. 



Hartman ('16) finds a similar structure in the egg of the 

 opossum, and describes it as a homogeneous, non-granular body 

 staining pink or lavender in iron ha?matoxylin, and bordered 

 by a light-colored band. 



The multinucleated eggs soon break up into a number of 

 fragments, often forming two or more parts very nearly of the 

 same size and often appearing like normal cleavage stages, 

 were it not for the presence of extra nuclei. Figs. 12, 13 and 14 

 show different stages in this process. 



The ultimate fate of the fragmented egg will now be considered. 

 Very early in the degenerative process, phagocytic cells are found 

 inside the zona pellucida, between the cytoplasm and the zona. 

 It is impossible to mistake these cells for fragments of either the 

 egg or polar bodies for they appear almost like transparent 

 vesicles with the deep staining nuclear material either scattered 

 as granules or irregularly clumped in a way which immediately 

 suggests their origin as polymorphonuclear leucocytes. Kingery 

 described similar cells but thought them of follicular origin. 

 The number of these phagocytic cells inside the zona varies, 



