92 THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 



migration is a misnomer, for the ovum does not make any great journey to reach the oppo- 

 site tube. I have not had the opportunity to study the relations of the pelvic organs in an 

 adult sow, but in large fetuses the ovaries may be quite close to each other; I have even 

 found them touching. It is likely that the fimbria? of the Fallopian tubes, which in the sow 

 are widely spreading and patulous, frequently reach both ovaries, and hence make it a 

 matter of chance which tube receives a given ovum. 



The question of the migration of the ovum has two aspects of immediate practical 

 interest. To the gynecological surgeon it is important to know that the extirpation of 

 one tube and the opposite ovary will not necessarily cause sterility. For the biologist the 

 subject brings up certain questions concerning the determination of sex, which will be 

 mentioned briefly. It is a very ancient theory that the production of two sexes of offspring 

 and their practically equal distribution in number are due to the formation of males by one 

 ovary, of females by the other, the left ovary usually being honored by the ascription of 

 female-producing potencies. This simple hypothesis is capable of proof or disproof by 

 numerous methods, which have not been wanting a trial, the most recent of such experi- 

 ments being those of G. H. Parker (1914), who adopted a very neat and ingenious plan of 

 experimentation. The method was to take an animal possessing a notably bifid uterus, 

 namely, the sow, and count the number of unborn pigs on each side with reference to sex. 

 Parker recognized the possible disturbing effect of migration of the ovum, though I think 

 to a far less degree than the facts warrant; and therefore he took large litters, and omitted 

 from his counts the pigs in the middle of the uterine horns, which may be thought most 

 likely to be the mixed product of the uterine horns, and counted only the two fetuses next 

 to each ovary and the two next the junction of the horns. The result, from the tabulation 

 of 1 ,300 pairs of fetuses, gave an almost absolutely equal distribution of the sexes on the two 

 sides. Now, at first sight it might seem that the great frequency of migration of the ovum, 

 which I have shown to exist, renders Parker's conclusions false, since they are based on the 

 general assumption that the embryos on one side of the uterus come from the corresponding 

 ovary. But, on the other hand, if it is true, as I believe, that the embryos in either horn 

 of the uterus are an inextricable mixture of the products of the two ovaries, then Parker's 

 figures can only be explained by the far-fetched assumption that exactly 50 per cent of the 

 ova migrate, or else that both sexes are equally represented in each ovary; the latter being 

 of course the conclusions already reached by Parker. 



CONCLUSIONS. 



In the foregoing paper the writer has given an account of the histology of the corpus 

 luteum of the domestic sow, remarking the presence of cells differing from the typical 

 lutein cells. 



A description is given of the canalicular apparatus and granules found in the lutein 

 cells, and it is shown that these structures undergo progressive changes during the course 

 of pregnancy. 



The microscopic appearance of the corpus luteum is described as it varies with the 

 advance of pregnancy. 



The corpus luteum of pregnancy is distinguished from that of ovulation by the more 

 regular and uniform morphology of the former, and the greater infiltration of fat in the latter. 



During pregnancy the Graafian follicles do not undergo the process of ripening, or 

 change of the theca interna which is preparatory to rupture. 



External migration of the ovum is a normal and very frequent occurrence in the sow. 



