On the CEstrous Cycle and the Corpus Luteum in the Sheep. 135 



" Preliminary Communication on the (Estrous Cycle and the 

 Formation of the Corpus Luteum in the Sheep." By F. H. A. 

 Marshall, B.A. Communicated by Professor J. C. Ewart, 

 F.E.S. Eeceived February 15 — Eead March 1, 1901. 



The sheep employed in this research were for the most part half- 

 breeds between Cheviots or Leicesters and Scotch Black-faced. Some 

 were very kindly kept for me by Professor Ewart at Penycuik, while 

 others were obtained from a neighbouring farmer, and killed at various 

 intervals after copulation. A quantity of material was also obtained 

 from the slaughter-house. In all these breeds the lambs are born in 

 February or March, and the ewes come into season in the following 

 October or November.* Yearling lambs are ready to take the ram 

 about the same time. 



Between March and October (period of ancestrum)f the uterus 

 remains in the normal condition (the resting stage). A large number 

 of ovaries from sheep killed in July and August were examined and 

 sections cut, but in no case were there seen either protruding follicles 

 or corpora lutea, or follicles beginning to undergo atresia. Moreover, 

 the walls of the Fallopian tubes showed no sign of congestion of the 

 blood-vessels. Ovaries from sheep killed in the middle of October 

 showed that the follicles were nearly approaching ripeness, this being 

 indicated by the extent of their protrusion, and a little later burst 

 follicles were first observed. From that time to the end of December 

 recently ruptured follicles in sheeps' ovaries were quite common. It 

 has been found impossible to draw any hard and fast line between the 

 procestrum and oestrus for sheep. The latter follows on the procestrum 

 very quickly, and the two combined are of short duration, probably not 

 more than two days. They will here be considered together, as 

 certain stages which appear to correspond to those which Heape 

 regards as forming part of the procestrum in other animals occur in 

 sheep at or even after the time of copulation. 



At the close of the period of ancestrum certain changes take place 

 in the external reproductive organs, the uterus, and the Fallopian 

 tubes. The vulva becomes distinctly swollen and congested, and I 

 have observed a slight flow of mucus from the external opening, but no 

 blood. Subsequent examination of the uterus has shown that bleeding 

 of the uterine wall is extremely slight, but it is, in some cases at any 

 rate, undoubtedly present. From an examination of the external 

 generative organs it is impossible to determine through what stage of 

 the period of growth or period of degeneration the uterus is passing, 



* Dorset sheep alone of British breeds have two gestations a year, 

 f Heape, " The Sexual Season in Mammals," ' Q. J. M. S.,' vol. 44, November, 

 1900. The terms "anoestrum," " dioestrum," &c, are here explained. 



