XIIl] 



FEMALE GENERATIVE ORGANS 



179 



period lasts for about three months and is succeeded by another 

 prooestrum . 



Polyoestrous animals diller from monoestrous ones in having 

 short recurrent cycles within a single sexual season. Thus in the 

 sheep the 'tupping time' may take place in autumn, and during 

 this season the ewe will experience a succession of cycles, each 

 lasting about 15 da3's, until jjregnancy is induced or tupping is 

 over; in the latter case the ewe passes into a state of prolonged 

 sexual quiescence (anoestrum) which lasts until the next tupping 

 season in the following autumn. The return of oestrus at short 

 intervals during the sexual season is implied a\ hen the shepherds 

 speak of the ewe as 'coming back' to the ram. 



pigment 





V 



5v'':-\.v;^^;;. 







Fig. 93. Section through uterine mucous merirbrane of sheei shewing pigment 

 fomied from extravasated blood (from Marshall). 



The short interval of rest between the 'heat' periods is called 

 by Heape the dioestrum and is characteristic of all polyoestrous 

 animals. In the sheep it lasts for about 12 or 13 days. It is followed 

 by a brief prooestrum when the ewe's external generative organs 

 become somewhat congested. There is however no external 

 bleeding in the ewe, and the uterine blood which becomes extra- 

 vasated during the prooestrum remains in the stroma, coming to 

 lie just below the epithelium Avhere it is converted into black 



