30 VETERINARY OBSTETRICS. 



twenty-four hours only, but appearing again every 

 fourteen days until the end of December. 



While these periods may be accepted as the 

 average, they are by no means definite, as some 

 animals, more especially high-tempered Mares, appear 

 always in heat ; while others again, the closest examin- 

 ation or manipulation fails to detect them in this 

 condition at any time, 



In a state of nature and free from artificial 

 surroundings, it may be accepted as a rule, that the 

 period of oestrum is so regulated that the young 

 animal may be born at a time of the year when its- 

 maintenance can be most suitably provided for in its 

 surroundings. 



If at this period contact with the male is allowed,, 

 certain changes take place which give rise to impreg- 

 nation. The spermatic fluid of the male animal, 

 either at or shortly after coition, finds its way to the 

 uterus of the female, and from the uterus the 

 spermatozoa enter the Fallopian tubes, and pass along: 

 to the ovarian termination of these structures. 



While it is generally believed that contact with 

 the ova of the female takes place in the Fallopian tube 

 and at its ovarian extremity, still we have occasionally 

 a foetus developed in the" ovary, and in this case at 

 least, impregnation must have taken place in the ovary- 

 and not in the tube. 



When impregnation has taken place, wherever it 

 may be, the impregnated ovum immediately afterwards 

 commences to descend the tube, gains the horn of the 

 uterus, becomes attached to the mucous membrane at 



