1903.] Formation of the Corpus Luteum in the Sheep, 355 



occur. The extra vasated blood retained in the mucosa forms pigment, 

 the change being effected by the agency of leucocytes, as supposed by 

 Bonnet, but not by Kazzander. But the extravasation occurs in the 

 superficial part of the mucosa. Miniature lacunse are sometimes 

 formed after extravasation. The severity of the procestrous process 

 tends to diminish with each successive dicestrous cycle in a season. 

 There is never any removal of stroma and not necessarily of epi- 

 thelium. 



The facts recorded render the homology between the dicestrous 

 cycle in the sheep and the menstrual cycle of the Primates very 

 probable, while further statements regarding the author's researches 

 on the ferret, with which the prooestrum in regard to severity is inter- 

 mediate between that of the sheep and menstruation in monkeys, 

 afford additional evidence of the identity of the two processes. 



Ovulation, with Notes on the Atretic Follicle and the Causes of Barren- 

 ness.— Ovulation can occur spontaneously at any cestrous (or pro- 

 cestrous) period with Scotch black-faced sheep, excepting at certain 

 oestri outside the regular sexual season, when the additional stimula- 

 tion supplied by coition may be necessary. In the ferret, ovulation 

 does not occur in the absence of coition, without which the follicles 

 undergo atresia. In the sheep, atresia is commonest in follicles of 

 about one-eighth to one-half the dimensions of the mature follicles. 

 When it occurs with any considerable frequency, it must affect the 

 barrenness percentage in subsequent breeding seasons. The atretic 

 follicle differs from the developing corpus luteum in the absence of any 

 discharge to the exterior, the membrana granulosa degenerating and 

 disappearing prior to any considerable ingrowth from the connective 

 tissue wall. 



The Formation of the Corpus Luteum. — The lutein cells are derived 

 from the membrana granulosa, while the connective tissue element 

 is supplied by the proliferation and ingrowth of the thecal interna 

 and externa, as described in the preliminary communication. Leuco- 

 cytes are abundant, especially at the sixteen-hour stage of develop- 

 ment, but these disappear in later stages without giving rise to 

 connective tissue as described by Sobotta. The cavity of the dis- 

 charged follicle is filled in by the further ingrowth of connective 

 tissue. 



