EMBRYOLOGY.

The Development of the Young.—We must here first speak of the ovum or germ, which is secreted by the ovary of the mare. Every time she comes in season (which occurs every three weeks during the hot weather) this ovum passes down the tubes before the womb as before mentioned, where it remains a few days and then dies if she is not put to the horse; but if, during the time this ovum is in the womb she is put to the horse and one of the spermatozoa from the semen of the horse comes in contact with it (the ovum) and a union of these takes place, then the rest of the semen dies and passes away, and the neck of the womb contracts gradually until it is perfectly tight. These two little bodies begin to grow when united and form the foetus, or foal. The foetus may be for convenience divided into three parts, viz.: the foetus proper, the navel string, and the placenta. The placenta is the part which is found covering the foal and is attached to the little pea-like elevations on the inside of the womb. This covering is found to be full of small blood vessels which finally unite to form two larger vessels, known as the navel veins. These carry the blood up through the navel opening of the foal and then to its heart. By the action of the heart it is forced all through the body of the foal and returned again to the heart. It is then forced down another artery to the navel opening, along the navel cord, into the placenta again, where it is distributed through the small blood vessels. When the blood comes down this cord from the foal it is in its impure state, and while it is passing through these small vessels in the placenta it comes very close to the small blood vessels in the womb. The blood is cleansed and nourished from the blood of its mother by a process similar to that which was spoken of when describing the lungs. The foetus, or foal, does not grow so fast the first month as it does later on. At the age of seventeen weeks the first hair appears on the lips and the tip of the tail. Between the thirty-fifth and the fortieth week the foal begins to show signs of life, and is completely covered with hair. After this time it grows very rapidly and may be seen moving around by watching the flank closely. The mare carries her foal eleven months, but in some cases an aged mare has been known to carry her foal over twelve months. In rare cases young mares may lack a few days of eleven months.

The Average Periods of Gestation of Domestic Animals.

Note—A mare having been served by a stallion may occasionally in the course of four or five weeks, manifest a desire for a second visit from the male; is again served and conceives both times. This is known as superfoetation. Such a case has been recorded by a veterinarian; the animal in question, a mare, giving birth to a horse colt and a mule colt, both dead. The mare had been covered by a jack and subsequently by a horse.

Signs of Pregnancy.—The veterinarian is occasionally called upon to give an opinion as to the pregnancy or non-pregnancy, of an animal and consequently should familiarize himself with the various indications which tend to prove the absence, or presence, of this condition. As a rule, when the mare conceives, heat, or the desire for the male, is no longer observable, and, on being led to the horse, she not only refuses to receive his caresses, but assumes the offensive, viciously striking and biting at him until led away. Soon the hair becomes more glossy, and the mare becomes quieter in disposition. This change is usually well marked in mares that are of a vicious disposition. The abdomen gradually enlarges as pregnancy advances, the right side being a little larger than the left. This enlargement is especially well marked in the cow. In some cases the beating of the foetal heart may be heard with the assistance of the stethoscope. Such an examination is, however, very likely to give rise to mistakes. After the eighth month well-marked symptoms of pregnancy are manifested, the belly at this time being considerably distended, the back sinking, etc. Before this time it is, however, impossible to make a positive statement as to the condition of the animal except by making a very close and thorough examination per rectum. The rectum should be cleared out by means of an enema (injection) of tepid water; the hand and arm should be well oiled and passed into the rectum. The region of the uterus being reached, an examination may be made of its condition. As the time for parturition approaches, the ligaments relax to a greater or less degree, and a well-marked depression or sinking in the lumbosacral region may be observed, the udder or bag enlarges, and milk is secreted. The secretion of milk sometimes appears long before the time of parturition, and has frequently been noticed to take place in animals that have never been bred. As a rule the animal shows slight uneasiness for a day or two before parturition, slight abdominal pain, etc., being manifested. About this time the vulva becomes larger, and presents more or less tumefaction. There may also be observed a flow of mucous taking place from the vulva for a day or two before parturition.