136 Mr. F. H. A. Marshall. On the (Estrous Cycle and 



nor has it heen, as yet at any rate, possible to state the duration of each 

 or all of these stages. The period of growth is marked by the hyper- 

 trophy of the uterine stroma by nuclear division, both in and between 

 the cotyledons. The nuclei in the early stages are distributed most 

 thickly in the region closest to the epithelium of the cotyledons. The 

 blood-vessels increase both in size and number, not at first so much in 

 the cotyledons as between them, and deeper in the stroma and in the 

 muscle layers below the stroma. The uterine cavity, never very large, 

 is at this period almost obliterated. The changes above mentioned 

 result in the breaking down of certain of the blood-vessels. The blood 

 corpuscles thus set free become scattered throughout the stroma, where 

 they form irregularly shaped patches and streaks lying a little below 

 the epithelium, but I have never seen spaces large enough to be 

 described as lacunae. These corpuscles no doubt go largely to form 

 pigment,* as supposed by Bonnetf and Kazzander.J Only in a few 

 places does the epithelium of the cotyledons, as seen in section, lose its 

 continuity, and then not more than four or five cells have disappeared. 

 Passing to such places may be seen small streams of blood corpuscles 

 which were being poured into the uterine cavity. Thus the charac- 

 teristics of all Heape's stages from I to Yl are more or less clearly 

 recognisable. 



The sheep, sections through the uterine wall of which show the last- 

 mentioned characters (stage VI), was killed within three hours after 

 coition. A Graafian follicle had just ruptured, as was at once appa- 

 rent from the bloodstain on its surface, but the blood had not yet 

 clotted. Subsequently cut sections revealed the point of rupture, and 

 also the ovum and discus proligerus, which had not yet been dehisced. 

 It was apparently from such a case as this that Hausmann§ drew the 

 conclusion that in sheep ovulation cannot take place without coition. 

 That this is not the case, at any rate for the virgin ewe at its first 

 oestrus, I subsequently proved. Some yearling lambs were kept along 

 with a ram which was rendered temporarily incapable of insemination 

 by the method generally followed by sheep breeders. The time when 

 the ewes came into season was indicated by their attitude towards the 

 ram. (Estrus having been detected by this means, the ewe in 



# Black pigment may not infrequently be observed, especially between and round 

 the bases of the cotyledons, beneath the uterine epithelium. In one case the 

 pigment was so distributed as to render the interior of the uterus perfectly black 

 between the cotyledons. I have never observed this pigment in the uterus of 

 yearling lambs. 



f Bonnet. See Ellenberger's ' Yergleichende Physiol, d. Haussaugethiere,' vol. 2, 

 Berlin, 1892. 



X Kazzander, " Uber d. Pigmentation d. Uterinschleimhaut des Schafes," ' Arch, 

 f. Mikr. Anat./ vol. 36, 1892. 



§ Hausmann, ' Ueber die Zeugung und Entstehung des wahren weiblichen 

 Eies,' &c, Hanover, 1840. 



