The temporary adhesion of the infundibulum to the surface of the ovary when an ovum is about to be discharged, appears to be ef fected by the interposition of a slimy mucus, which possesses sufficient tenacity to require the employment of some slight force in draw ing the parts asunder, and which is furnished, probably, by those numerous minute folds or plicm so plentifully covering this portion of the tube.
It was formerly supposed that this ap position of the mouth of the tube to the ovary occurred only under the influence of the sexual orgasm ; an inference which was natural so long as the belief remained general that the ova were discharged from the ovary only as a consequence of sexual congress. But this circumstance admits of a modified explanation, now that the discharge of the ovum in mammalia is known to occur during the "heat," or that period in which alone the coitus is permitted by the female. The ap position of the Fallopian tube to the ovary at such times is to be regarded as a move ment providing for the safe passage of the ova to the uterus, and, in regard to time, as preceding the act of impregnation, although it might endure until after a fertilising coitus had taken place, and so the parts would occasionally be found in such a state of apposition in an animal killed immediately or shortly after that event ; thus appearing to warrant the conclusion that the venereal orgasm had been the cause of this movement. The mode in which the ovum is expelled from the ovary has been already described at p. 560. In the form there represented, the ovum is received into, and is conducted along, the Fallopian tube ; and, on account of the interest which attaches to the earlier deve lopmental changes occurring here, it has, perhaps, been more frequently examined in this situation than in any other portion of the generative track. Barry's tables include the particulars of ninety-three ovula, found in various parts of the tube in the rabbit, between 10 and 70 hours post coitum. Bischoff's observations were made upon 60 or 70 ovula within the tube in the same animal, as well as upon many more in other mammalia. Several instances of the same kind have been already quoted, two of these being in the human subject; and almost every anatomical collection contains examples of the human ovum abnormally arrested and developed in the tube.
In what way the ovum, after its reception by the mouth of the tube, is conveyed along that canal into the uterus, is explained by the peculiar construction of this part. The tube
being lined longitudinally by slender folds which divide it into numerous capillary canals, and having every part of its inner surface co vered by cilia, vibrating, according to Henle, in a direction towards the uterus, appears admirably adapted for the conveyance of the minute ovum downwards from the place of its formation to its seat of normal develop ment. The peculiar form of the oviduct, which is more or less funnel-shaped, especially in the human subject, further conduces to this direction of the ovum downwards, while, in many instances, its course appears to be aided by that peristaltic action of the walls of the tube which many observers have noticed, and of which a further account will be presently given.
The period of time occupied by the de scent of the ovum through the tube does not usually exceed a very few days. This, how ever, appears to be a variable feature in different mammalia, and regarding which, even in those animals admitting of the readiest observation, it appears very difficult to arrive at definite conclusions, chiefly on account of the uncertainty belonging to the determination of the precise moment at which the ovum quits the ovary.
In the bitch the ovum, after quitting the ovary, is supposed to remain in the tube susceptible of impregnation during 6 or 8 days; and its passage is probably quite completed in 10 days. In the guinea-pig the ovum makes its passage in a much shorter time, as it usually enters the uterus at the end of the third day. In the rabbit the time is nearly the same. The ovum, surrounded by a thick layer of albumen, passes from the oviduct into the uterus at the end of the third or beginning of the fourth day. While in the roe, although the time occupied is probably longer, yet, at the most, in a few days, the ovum, unaltered in size, as in other cases where it receives no albumen in the tube, reaches the uterus, and there, if impreg,na tion has taken place, it remains four and a half months without undergoing any positive change. In man little is known accurately respecting the time occupied by the passage of the ovum through the tube. Omy two instances have been recorded in which the human ovum has been actually seen in the tube (see p. 567.), with the exception of ab normal cases.