CYCLIC CHANGES IN THE OVARIES AND UTERUS OF THE SOW, 

 AND THEIR RELATION TO THE MECHANISM OF IMPLANTATION, 



1. GENERAL. 



INTRODUCTION. 



The undertaking set forth in these pages is simple in plan, namely, to follow 

 in one mammal (the sow) the anatomical changes in uterus and ovary which under- 

 lie the reproductive cycle. The prospective value of such a study may deserve a 

 word of explanation; it arises from the fact that in different organisms there are 

 varying forms of expression of the cyclic sexual processes. Even within the order 

 of mammals, the reproductive cycle of the female is obscured by as yet unresolved 

 dissimilarities and no satisfactory correlation has been made between phenomena 

 so unlike as the urgent rutting of deer, the inconspicuous oestrus of rodents, and the 

 menstrual cycle of the catarrhine apes and man. In our own species we have only 

 conflicting conjectures as to the time of ovulation and the meaning of menstruation, 

 although exact knowledge of this subject would be of value not only for its own sake, 

 but also for the calculations of the embryologist and the gynecologist. The need, 

 therefore, is for a detailed study of individual species, including the determination 

 of the oestrous period and the time relations of ovulation, growth, and retrogression 

 of the corpus luteum, tissue changes in the uterus, and the progress of the ova, 

 whether fertilized or unfertilized. 



Some such account has been pieced together for five species, though not with 

 equal completeness: a marsupial, Dasyurus viverrinus (Hill and O'Donoghue, 1914); 

 the rabbit (Niskoubina, 1909; Ancel and Bouin, 1910; etc.); the guinea-pig (Loeb, 

 1911, 1914; Stockard and Papanicolaou, 1917; Ishii, 1920); the rat (Long and 

 Evans, 1920-1921) 1 ; and the dog (Marshall and Jolly, 1906; Marshall and Hainan, 

 1917; Keller, 1909). Something is known of the cycle of ovulation but not of the 

 uterine changes in several other mammals, while in man we know much about the 

 histological cycle of the uterus and almost nothing of the ovarian sequence. 



Choice of the domestic pig as subject for a similar study was determined by 

 a combination of circumstances which seemed to outweigh the disadvantages of 

 large size and commercial restrictions upon the collection of material. In 

 this animal oestrus is regularly periodic, frequent, and outspoken; ovulation is 

 spontaneous; study of the ova and embryos is facilitated by the large litters; 

 the ovaries of the ungulates are notably uncomplicated, as contrasted, for instance, 

 with those of the rodents; and the uterine mucosa is of the non-deciduate type, 



1 1 am indebted to Professors Long and Evans for the opportunity to study in manuscript their forthcoming definitive 

 account of the oestrous cycle of the rat, based on their preliminary studies referred to in the appended bibliography. 



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