io6 THE PHYSIOLOGY OF REPRODlfCTION 



than in the deeper tissue. Thus, although leucocytes are probably 

 involved in the process of pigment formation, there is no need to 

 assume that they carry the extravasated corpuscles to the region 

 where pigment is most abundant. Sometimes the interior of the 

 uterus appears superficially to be perfectly black with pigment, but 

 in such cases the pigment is, no doubt, derived from blood which 

 had been extravasated during a series of prooestrous periods, and 

 not merely during the most recent one. Assheton ^ states that the 

 pigment so formed is subsequently disposed of. 



Corner^ has described cyclic changes in the uterus of the sow. 

 Just before oestrus there is evidence of activity on the part of the 

 epithelial cells in which mitotic figures may be found, while a contrary 

 process is manifested here and there in nuclear chromatolysis and 

 degenerate changes, and neutrophilic polymorph leucocytes in the 

 sub-epithelial stroma become very numerous. During oestrus the 

 stroma is very oedematous. The post-oestrous changes are very 

 marked. The epithelial cells actively secrete a serous fluid from the 

 eighth to the tenth day, after which they subside to a cuboidal form, 

 and there is a slow reversion to the cestrous type. Post-oestrous 

 glandular hypertrophy is not definite, but otherwise the changes are 

 clearly suggestive of an abbreviated pseudo-pregnancy occurring 

 under the influence of the corpus luteum of the ovary (see above, 

 pp. 99-101, and below, pp. 371-372). 



The Cycle in Marsupials 



The changes which occur in the internal generative organs of 

 the Marsupial cat {Dasyurus viverrinus) have been described fully by 

 Hill and O'Donoghue (see p. 36). The prooestrum lasts for from 

 four to twelve days, and during this time the uterine mucosa 

 increases in thickness and becomes more vascular, while its glands 

 lengthen and become convoluted and the epithelium tends to 

 thicken. During oestrus, which lasts one or two days, the changes 

 above described are continued. Following oestrus there is, according 

 to these authorities, a post-oestrous period lasting five or six days 

 and terminated by ovulation, and during which the uterine changes 

 continue further. This is followed by either pregnancy or pseudo- 

 pregnancy. During pseudo -pregnancy the uteri enlarge considerably 

 and become still more vascular, and these changes are succeeded by 

 degeneration and desquamation of epithelium with extravasation of 



1 Assheton, "The Morphology of the Ungulate Placenta," Phil. Trans., B., 

 vol. cxcviii., 1906. Changes in the uterine mucosa have also been described in 

 pigs. See Steyn, Oster. Wsckr.f. Tierheilhmde, 1912 ; and Geist, 1913, loc. cit. 



2 Corner, "Cyclic Changes in the Ovaries and Uterus of the Sow, etc." 

 Contributions to Embryology, No. 64, Carnegie Institute (Washington) Publica- 

 tions, 1921. 



