FATE OF UNFERTILIZED EGG IN WHITE MOUSE. 329 



eight or ten being the largest number found. These cells prob- 

 ably aid in the disintegration of the periphery of the cell. This 

 process may begin some time before fragmentation sets in, as is 

 evidenced by a study of Fig. 9. Here the space at one end of 

 the egg filled with dark granules indicates that the cytolysis of 

 the cytoplasm has begun. 



The zona persists in nearly all cases as far as the eggs have 

 been followed. Fig. 6 shows one of the exceptions, for here the 

 zona is gone and many dark staining fragments which may have 

 come either from the polar body (which is now very small) 

 or from the broken down zona, are seen surrounding the egg. 

 Several phagocytic cells, one of which is figured, are to be seen 

 among the fragments. Although the zona is present in almost 

 all cases, a careful examination usually brings to light several 

 breaks, and it is probably through these that the phagocytic 

 cells are able to reach the egg. 



Figs. 19 and 20 show the last stages in the disintegration and 

 absorbtion of the fragments by the phagocytes. Some of the 

 fragments appear as mere shells with only occasional granules, 

 while the outer edge of others shows a honeycombed condition 

 due to excessive vacuolization. 



It is found that the unfertilized egg completes its passage 

 through the Fallopian tube and enters the uterus about the 

 end of the third day or almost at exactly the same time as 

 given by Sobotta for the normal segmenting egg. 



Smith ('17), basing ovulation as occurring twenty hours after 

 parturition, finds that unfertilized eggs of the mouse enter the 

 uterus about 76 hours after ovulation and are found in the last 

 fold of the uterus at 88 hours. 



The final dissolution of the fragmented egg evidently is com- 

 pleted early on the fourth day, since out of eleven mice older 

 than four days, all showing corpora lutea in the ovaries, indi- 

 cating that ovulation had taken place, in only three could eggs 

 be found. A single egg was found in the uterus of a mouse one 

 hundred and five hours after parturition (Fig. 18). 



In not a single case has anything approaching a cleavage 

 spindle as described in atresic ova by Spuler, Loeb or Newman, 

 been observed, but it is not to be interpreted that they may 



