GESTATION. The gestatory term in quad rupeds is much regarded by their bulk. In the elephant it is about 20 months, in the camel between 11 and 12, in the mare and ass the same. According to the observations of M. Teissier of Paris, in 582 mares, which copulated but once, the shortest period was 287 days, and the longest 419; making the extraordinary difference of 32 days, and of 89 days beyond the usual term of 11 months. The cow usually brings forth in about 9 months, and the sheep in 5. Swine usually farrow between the 120th and 140th clay; being liable to variations, influenced appar ently by their size and their particular breeds. In the bitch, on the contrary, be she as diminu tive as a kitten, or as large as a boarhound, pupping occurs on or about the 63d day. The cat produces either on the 55th or 56th day. The true causes which abridge or prolong more or less the period of gestation in the females of kept as a breeder it is better that she drop her first colt at three years old, and then rest one year, so as to produce the next colt at five years of age, and yearly thereafter ; and since the mare goes with young eleven months, care must be taken that she does not go over the first heat before being again served. Most mares will receive the boric on the ninth or tenth day after foaling, and this period should never be allowed to pass • over without her being shown the horse. Some of these results do not alto gether coincide with the results of observations in England, where, for example, July, the sea• son of copulation for the cow, is considered too late. That period would produce late calves in tilt following year. November is stated to be the best season for the ewe; for the black-faced ewe it is, but for the Leicester, and, in many situations, for the Cheviot ewe, it is a month too late. The duration of the power of quadrupeds, and of the incubation of birds, are yet unknown to us. Many persons are also unacquainted with the proper age for reproduc tion, and the duration of the power of reproduc tion, and other conditions even of the domesti cated animals. It can not, therefore, but be interesting to find iu the following table the results of observations made on this subject by the best ancient and modern naturalists. The development of the reproductive powers of farm animals differs widely, both as to the age, when they begin to breed, as well as their time of carrying their young. The sow will breed at one year old, the period of gestation being 113 days. The ewe breeds at fifteen months, and carries the young 152 days. The cow will breed
at two years old, and if well kept may be put to the bull at fifteen months of age, since she car ries young nine months. The mare is usually not bred until the age of four years, but if to be reproduction accords with our experience as respects the mare and stallion; but 13 years of age for the cow, and 8 for the bull, is too.young a period for old age in them, fine animals of both sexes, of a valuable breed, having been kept in-a useful state to a much greater age. I have seen a short-horn bull in use at 13 years, and a cow of the same breed bearing calves at 18; but if the ages of 8 and 13 respectively refer to the usual time bulls and cows are kept for use, the statement is not far from the truth. From some carefully collected and very exten sive notes made by Lord Spencer on the periods of gestation of 764 cows, it resulted that the shortest period of gestation, when a live calf was prpduced, was 220 days, and the longest 313 days, but he was not able to rear any calf pro duced at an earlier period than 242 days. From the result of his experiments, it appears that 314 cows calved before the 284th day, and 310 calved after the 285th; so that the probable period of gestation ought to be considered 284 or 285 days. The experiments of M. Teissier on the gestation of cows, are recorded to have given the follow ing results. 21 calved between the 240th and 270th day, the mean time being 259i days; 544 calved between the 270th and 299th day, the mean time being 282 days; 10 calved between the 299th and 321st day, the mean time being 303 days. In most cases, therefore, between nine and ten months may be assumed as the usual period; though, with a bull-calf„ the cow has been generally observed to go about 41 weeks, and a few days less with a female. Any calf produced at an earlier period than 260 days must be considered decidedly premature, and any period of gestation exceeding 800 days must also be considered irregular; but in this latter case, the health of the produce is not affected. Mr. C. Hilliard, of Northampton, Eng.,states that the period of gestation of a cow is 284 days, or, as i,t is said, 9 calendar months and 9 days; the ewe, 20 weeks; the sow, 16 weeks; the mare, 11 months. The well-bred cattle of the present time would seem to bring forth twins more fre quently than the cattle did fifty years ago, prob ably the result of better care and feeding. The males of all animals, hares excepted, are larger than the females. Castrated male cattle become larger animals than entire males.