46 WALTER HEAPE. 



one to four days ; in the bitcli seven to twelve days (Stone- 

 henge, 1887) ; in the chimpanzee six to eight days (Keith, 

 1899). In cattle and sheep the external evidence of pro- 

 oestram is difficult to determine, and oestrus appears to follow 

 very quickly upon the former, about oue day after or less. 

 Pigs, on the other hand, exhibit external signs of pro-oestrum 

 somewhat longer, while mares are very variable in this respect. 



A further consideration of the subject is divided into the 

 external and internal evidence of pro-oestrum. 



The External Evidence of Pro-oestrum in Mam- 

 mals. — The first sign of pro-oestrum noticed, in the lower 

 mammals, is a swollen and congested vulva, and a general 

 restlessness, excitement, or uneasiness. There are other 

 signs familiar to breeders of various mammals, such as the 

 congested conjunctiva of the rabbit's eye, and the droop- 

 ing ear of the pig, which are considered by some as even 

 more reliable indications of the probability or capability 

 of conception than is afforded by the vulva alone. Many 

 monkeys (Heape, 1894, 1897, Keith, 1899) exhibit conges- 

 tion of the face and nipples, as well as of the buttocks, thighs, 

 and neighbouring parts; sometimes they are congested to a 

 very marked extent, and in some species a swelling, occa- 

 sionally prodigious, of the soft tissues round the anal and 

 generative openings, which is also at the time brilliantly 

 congested, indicates the progress of the pro-oestrum. 



The Pro-oestrous Discharge and Menstrual Flow. 

 — Following the swelling and congestion of the external 

 generative organs, there is, in most animals, a discharge from 

 the generative canal. The discharge may consist merely of 

 mucus from the uterine glands and from the glands of the 

 cervix and from those in the neighboui-hood of the vaginal 

 orifice, of the products derived from the breaking down of 

 epithelial tissue, and of fragments or small masses of pave- 

 ment epithelium from the vagina; such a discharge is usually 

 to be seen in the rat and mole. 



In addition, fragments or small masses of columnar uterine 

 epithelium may be observed in various animals. Again, to 



