354 Mr. F. H. A. Marshall. The (Estrous Cycle and the [Feb. 17, 



true order of events. The haustoria have been formed by the hyphse, 

 and figures are given showing every stage in their development. The 

 first haustorium may be formed by the infecting tube immediately 

 after its penetration through the stoma, and figures are given showing 

 the remains of the germ-tube outside a stoma, the swelling of its tip 

 over the stoma into an appressorium, the passage through the stomatal 

 cavity, and its development into a vesicular swelling whence the true 

 infection tube arises, which latter may at once put forth a haustorium. 

 In some cases all these latter phenomena are visible in one and the 

 same preparation. 



The author expresses his thanks to Miss E. Dale, of Girton 

 College^ for valuable aid during the later stages of the work, in the 

 embedding and cutting of numerous sections. 



" The (Estrous Cycle and the Formation of the Corpus Luteum in 

 the Sheep." By Francis H. A. Marshall, B.A. Communi- 

 cated by Professor J. C. Ewart, F.B.S. Beceived Febru- 

 ary 17 —Bead March 12, 1903. 



(Abstract.) 



Introduction. — A preliminary account of this investigation was 

 communicated to the Boyal Society in 1901, and published in the 

 Proceedings for that year. Subsequently the work has been carried 

 further, and recently brought to a conclusion. 



The (Estrous Cycle. — In Scotch black-faced sheep the length of the 

 sexual season is shown to vary with the locality, both in regard to the 

 number of dicestrous cycles in a season, and to the duration of each 

 cycle. It is shown further that there is a perfect gradation between 

 the moncestrous condition of some wild sheep to the extreme poly- 

 oestruni of certain Merinos. 



Superficial Phenomena of Promstrum and (Estrus. — The procestrum is 

 marked by a mucous or sanguineo-mucous flow. It is very rapidly 

 succeeded by oestrus (the period of desire), the two periods fre- 

 quently seeming to occur simultaneously, but this is because of the 

 abbreviation of the process. 



The Histology of the Uterus during the Dicestrous Cycle. — The changes 

 through which the sheep's uterus passes during a single dicestrous 

 cycle can be divided into four groups or periods, as follows : — 

 (1) Period of rest; (2) Period of growth and increase of vessels; 



(3) Period of breaking down of vessels and extravasation of blood ; 



(4) Period of recuperation and pigment formation. Bleeding into the 

 uterine cavity and at the external genital aperture does not always 



