126 CYCLIC CHANGES IN THE OVARIES AND UTERUS OF THE SOW, ETC. 



nation. Corner and Amsbaugh (1917) concluded, from a study of 10 animals, 

 that ovulation probably occurred on the first or second day of osstrus; but the 

 exact time of onset of heat in these animals could not be stated with great exactness, 

 since the pens were visited but twice daily, and in some cases less often. A some- 

 what different conclusion is drawn by Lewis (1911) from the results of his experi- 

 ments, unfortunately not known to us at the time of our work. His material con- 

 sisted of 23 sows, in which the onset of heat and the time of copulation were noted 

 with exactness, the animals being killed at varying times thereafter. In those 

 killed before 30 hours after onset of cestrus the follicles were not ruptured (with 

 one exception), but in most of those killed between 30 and 48 hours the follicles 

 had collapsed. In one case ovulation had not occurred at 70 hours, but as no 

 microscopic examination is mentioned, we can not exclude the possibility that this 

 last case is one in which the follicles had undergone atresia instead of rupture. 

 Lewis's interpretation is that "the ovum (in hogs) is not liberated from the -ovary 

 until the last part of the period of heat, " but from his table one is forced, rather, 

 to conclude that ovulation usually occurs during the second day of the period of 

 restrus. 



FATE OF THE OVUM: PASSAGE AND ATTACHMENT OF THE EMBRYOS. 



The time necessary for the passage of the ovum through the Fallopian tube 

 has been set by Assheton (1898) at 3 days, and the present writer's findings are in 

 accord with this statement. This journey of 18 or 20 cm. is therefore traversed in 

 the same time as the far shorter distance in a small mammal like the mouse. If 

 copulation has occurred, the conjugation of ova and spermatozoa takes place in the 

 Fallopian tube and segmentation reaches the stage of 2, 4, or 6 blastomeres by the 

 time the uterine end of the tube is reached. About the fourth day the ova enter 

 the uterus. 



Much interest attaches to the fate of the ova when copulation does not occur. 

 Degenerating ova are but rarely found in the tubes, and one is therefore forced to 

 suppose that all the ova pass into the uterus, whether or not the sow has been 

 impregnated. This conclusion is strengthened by the fact that if from the run of 

 sows at the abattoir one selects those whose ovaries contain fresh-looking solid or 

 nearly solid corpora lutea (i. e., 5 to 7 or more days after ovulation), a considerable 

 proportion of these will be found, upon careful search, to contain either normal- 

 looking or degenerating unfertilized ova in the uterus. Scores of such obser- 

 vations, confirmed in numerous cases by microscopic estimation of the age of the 

 corresponding corpora lutea, make it seem clear that the unfertilized ova regularly 

 pass into the uterus and degenerate there, not disappearing completely, however, 

 before at least the seventh day after ovulation. 



Some information as to the probable time of their final dissolution can be 

 obtained from the following table of cases in which the ova were sought in the uteri 

 of animals whose last cestrous period had been observed, and which had not been 

 impregnated. 



