THE "SEXUAL SEASON OP MAMMALS. 7 



''oestrum ; " as 1 have before remarked^ some of these terms 

 are used also to designate the rutting season of the male, and 

 most of them are used indiscriminately for both the periods 

 of pro-oestrum and oestrus, which I seek now to establish 

 for the female. In comparing, therefore, the writings of 

 former investigators with the statements made in the follow- 

 ing- paper, it must be recollected that the various terms 

 hitherto used are not necessarily homologous with those used 

 by me, and are not necessarily descriptive of the sexual 

 season or of the breeding season of female mammals, as I 

 understand these processes. Much of the confusion and 

 misunderstanding which exists, regarding breeding phe- 

 nomena, is due to the indiscriminate use of the terms above 

 noted, and it is essential that their use should be restricted, 

 or given up altogether. 



There is one point which I should briefly refer to here. I 

 have said above that oestrus, the period of desire, normally 

 follows pro-oestrum; but there are times when the females of 

 certain, probably of many, mammals are anxious to receive 

 the male without the pro-oestrum having taken place. 



This condition may occur in various mammals during 

 pregnancy, and has frequently been noticed in most species 

 of domestic mammals during that period, while it is evident 

 in a considerable number of animals also at other times. This 

 may be called abnormal oestrus. Normal oestrus, as we 

 shall see below, occurs in conjunction with certain changes 

 in the uterine tissue, and this is accompanied by congestion 

 and stimulation or irritation of the copulatory organs; 

 whether the congested condition of the latter organs is in 

 itself sufficient to induce oestrus, or whether the presence of 

 some peculiar substance in the blood, or other infl.uences, are 

 essential for that purpose, is not known ; however that may 

 be, congestion is invariably present, and is an essential 

 condition. 



So also in abnormal oestrus, congestion of the copulatory 

 organs takes place, but the changes in the uterus which are 

 evident in normal oestrus are apparently absent. When 



