Changes in Generative Organs, etc., of Non-Pregnant Dog. 557 



Conclusions. 



The uterus and mammary glands of the non-pregnant Bitch undergo 

 pronounced postoestrous development under the influence of the corpora lutea, 

 there being a definite pseudo-pregnant period. 



Retrogressive changes do not set in with any of these organs until about 

 30 days after ovulation, and in the case of the mammary glands a somewhat 

 later period. 



The developmental changes are of a similar kind to those taking place 

 during pregnancy, but do not reach the same degree of development. 



The entire series of changes are physiologically homologous with the 

 changes shown by the uterus and mammary glands of the pseudo-pregnant 

 Eabbit and Marsupial Cat. 



The relatively long persistence of the corpora lutea in the Bitch is probably 

 correlated with the moncestrous habit. 



This persistence, which is possibly greater in some individuals than in 

 others, elucidates the not uncommon phenomenon of bitches which had not 

 been impregnated secreting milk at or near the end of the pseudo-pregnant 

 period. 



The changes which occur in the generative organs and mammary glands 

 after oestrus are now brought into relation with the rest of the oestrous cycle, 

 and the complete cycle in the Bitch may be summarised in the following 

 scheme : — 



The terms pro-oestrum, oestrus, and ancestrum are those originally proposed 

 by Heape, and represent the periods so described by him. The first part of 

 the ancestrum is generally occupied by the nursing or lactation period, but in 

 the case of animals which have experienced pseudo-pregnant conditions the 

 lactation period is usually only very imperfectly represented. The metcestrous 

 period must now be regarded as unrepresented in the Bitch. It exists in 

 animals which do not experience pseudo-pregnancy {e.g. in those rabbits in 

 which corpora lutea are not formed after oestrus). 



The work was carried out at the School of Agriculture and Field 

 Laboratories, Cambridge. The expenses were defrayed largely by a grant 



Pro-cestrum 



CEstrus 



'-pregnancy 



Ancestrum 



