THE FATE OF THE UNFERTILIZED EGG IN THE 



WHITE MOUSE 



HARRY H. CHARLTON, 

 OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY. 



It has long been known that in mammals many more eggs are 

 ovulated than develop into embryos, due in part to the failure 

 of the spermatozoa to reach them, and perhaps more often to 

 the inability of the eggs to implant themselves in the uterus. 

 Such eggs are said to degenerate, but the story of their fate has 

 been recorded in only a few instances. Since ovulation in 

 the mouse is independent of copulation, this animal was se- 

 lected for the investigation. It is natural to suppose that the 

 process would be similar to the degeneration of the ovarian egg 

 which has been prevented from leaving the ovary, the process 

 termed follicular atresia. 



The atresia of ovarian eggs in mammals has been described 

 in detail by many investigators, but the degeneration of the 

 unfertilized egg in the Fallopian tube and uterus has been given 

 but little special study. Heape ('05) working on the domestic 

 rabbit, mentions the finding of eggs in the tube which for some 

 reason or other had not been fertilized and were in a process of 

 degeneration. Hartman ('16), in his study of the early develop- 

 ment of the American opossum, also refers to the great number 

 of unfertilized eggs, approximately 50 per cent., which he found 

 in the uterus, in an earlier or later stage of degeneration. He 

 ventures the opinion that these eggs would eventually leave the 

 uterus. 



Students of atresia have usually recognized that there is an 

 early disturbance of the nucleo-cytoplasmic relationship, although 

 they have not always given it that name, and that it was followed 

 by a rearrangement of the cytoplasm. Some writers however 

 insist that a true parthenogenetic cleavage may take place, and 

 continue in a more or less normal manner up to, in some cases, 



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