GESTA TION. 



139 



The differences in individuals of the same breed or species may be 

 partly accounted for by the fact, that impregnation is possible at any 

 time during oestrum — a variable period ; and if coitus has taken place 

 several times during this condition, it is impossible to predict when con- 

 ception took place. And even when contact has only occurred once 

 between the male and female, fecundation does not necessarily coincide 

 with this intercourse ; as the ovule may meet the spermatozoa in differ- 

 ent regions of the uterine system, and may therefore only be fertilized 

 some days after copulation. The time required for the ovule to pass 

 through the Fallopian tube also varies in different animals. In the 

 Rabbit and Guinea-pig, for instance, it takes three days ; in Ruminants 

 from four to five days, and in the Bitch from eight to ten days. 



And, as has been remarked, various circumstances may retard or 

 accelerate the development of the foetus ; not only this, but with some 

 animals it may apparently remain for a number of days in the uterus 

 after it is ready for birth, without inconvenience to the mother or itself, 

 just as it may be born several days before the ordinary period without 

 compromising its safety. 



For these reasons, the period of gestation can only be approximately 

 fixed, though there are of course limits beyond which Nature, ever 

 provident and watchful for the preservation of species, cannot go with 



ceasing to be natural. 



Mare. 



The usual period of gestation with the Mare is eleven mo?iths, though it 

 may vary between ten and twelve. 



From the observations of Winter, Brugnone, Tessier, and Grille, in 

 284 Mares, it results that the shortest period of gestation in this animal 

 was 307 days, and the longest 394 days — or a mean duration of 346 days. 



Gayot, in 25 instances noted at the Haras of Pin, France, found the 

 average to be 343^ days ; the shortest being 324 days, and the longest 

 367 days. 



A writer in the Jourjial d' Econofnie rurale beige for 1829, cited by 

 Rainard, gives as the minimum 322 days, maximum 419 days, the aver- 

 age being 347 days. 



Colin gives the average as 345 days, though birth may occur at the 

 330th to 365th, and sometimes to the 380th day. 



Dieterichs gives the shortest period as 307 to 317 days, and the longest 

 as 409 to 419 days — the average being 336 to 342 days. Baumeister 

 and Rueff give a minimum of 330 days, or eleven months, the maximum 

 as 420 days, or fourteen months* — the average as 340 days, or 11^ 

 months. 



With regard to the influence of breed on the duration of pregnancy, 



* H^mon {Recueil de Med. Veterinaire, 1867) alludes to the case of a Mare seven years old, which 

 went beyond her ordinary period of pregnancy, only manifesting at the usual time the customary signs of 

 foaling ;' though these soon ceased, but recurred again in fifteen days, only to disappear in a short time. 

 After this interval the animal appeared to be quite well, feeding and working as before. At the seventeenth 

 month of pregnancy she was in the same condition ; but on the fifteenth day of the eighteenth month, 

 she was siezed with serious symptoms which continued during four days, when death ensued. Hamon 

 examined the body in the presence of many people, who were much interested in the case, and discovered 

 a foal which weighed 75 kilogrammes, and was as fat and fresh-looking as if it had been extracted at the 

 normal period. The tongue protruded from the mouth, the eyes were almost gone, the muscles were well 

 developed but somewhat bloodless, and the position of the foetus was natural. The umbilical cord had the 

 same aspect as in ordinary cases, but there was no Wood in its vessels, and it was ruptured at five or six 

 centimetres from the abdominal walls. The foetal envelopes were hypertrophied, their total thickness being 

 four to five centimetres; otherwise they were healthy. The cervix uteri was of a great thickness and 

 very rigid ; when dilated it would only allow the passage of the list. The liquor aninii was reddish-colored. 



