We must remark, however, that when a female quadruped is opened immediately after copulation, the 1iinbrize are frequently not olkerved to be in contact with the ovary ; and this is found to be the case only when some hours are allowed to elapse between the copulation and the death of the animal. Ilaighton never found it to have taken place in the rabbit previous to nine hours after union with the male, and De Graaf not even before twenty-seven hours ; but observations of this nature upon animals opened soon after being killed, do not make it certain that the action had not taken place; for it may be supposed that the adhesion between the infundibula and ovaries had commenced, but was less firm than it becomes at a subsequent period, and that it was merely disturbed by the violence of the death or rough handling of the body. This is the more probable, seeing that the same change of position has been observed to take place before sexual union in animals in the state of heat, as by Cruikshank in the rab bit, and by Haller in the sheep. In some birds, particularly domestic fowls and ducks, it is well known that when they are well fed all the changes necessary for the formation of an ovum and its discharge from the ovary may take place without the concurrence of the male, and in quadrupeds there is reason to believe that the turgescence and change of position of the generative organs above alluded to may fre quently occur independently of fruitful or un fruitful sexual union, as from excitement of the generative organs in the state of heat, or as in the cases observed by Haller, of ewes having connection with wedders or castrated males only.
There is every reason to suppose that the same changes which we have described as oc curring in quadrupeds after sexual union, take place in the same circumstances in the human female ; that is, that the fimbriated infundibula of the Fallopian tubes are brought near to the ovaries, and are made to embrace them firmly, so as to receive the contents of any vesicles which may burst ; and that this change is produced by an action which begins usually during sexual union, but which may also occur without any venereal orgasm.
The ovaries, we have already stated, become unusually vascular during and after sexual union ; but the changes in the ovary which most demand our attention, are those connected with the bursting of the Graafian vesicles, and the discharge of their contents. In the unim pregnated female arrived at the age of puberty, the Graafian vesicles of the ovary are of une qual size. Some time after sexual uninrf, one or more of these vesicles, probably those which are at the time farthest advanced, undergoes a greater enlargement, and from its swelling pro jects beyond the rest of the surface of the ovary, and after various other changes, an aperture is formed in the most projecting part of the coats of the vesicle, through which its contents find an issue. But before proceeding further with this narrative, we must recall to the recollection of the reader the nature of the ovum, which, on the occasion of the rupture of one of the Graafian vesicles, is discharged from its inte rior.
The ovarian vesicles of man and quadrupeds are filled with fluid, which, viewed by the un assisted eye, appears to contain only a little granular and flaky matter. This fluid is coa
gulated by heat, alcohol, or acids, as albumen is, and also by expoure to air. The membrane forming the vesicle consists of two layers, an external and internal, and the whole vesicle is covered also by the general peritoneal and vas cular envelope of the ovary.
From the earliest times anatomists and phy siologists seem to have considered the ovarian vesicles as the source of the offspring; and many, from a sort of loose analogy with ovipa rous animals, regarded the vesicles themselves as the ova in which the viviparous foetus is de veloped. The large size of these vesicles, how ever, as compared with the Fallopian tubes through which the ova have to pass, and the subsequent observations of De Graaf, Vallisneri, and Cruikshank, as later those of Prevost, Dumas, and others, who found in the first days after copulation ova in the Fallopian tubes of a size considerably less than the vesicles of the ovary from which they had proceeded, proved satisfactorily that the ovarian vesicles and ova are not identical. Various conjectures were in the meantime offered by different authors as to the source of the ovum ; some holding it to be formed by a process of secretion, others by an organic union of the male semen with the contents of the Graafian vesicle, and so forth ; but no one ever observed the ovum itself of mammiferous animals within the ovary, until Baer made this important discovery in 1827, by the examination with the microscope of the fluid contents of the Graafian vesicle•' Baer found that, in the centre of a granular layer, placed generally towards the most promi nent part of the vesicle, to which he gives the name of proligerous disc or layer, there is fixed a very minute spheroid body, seldom above part of an inch in diameter. The appear ance of this body he found to be constant, and on examining it with attention in the vesicles of the ovaries, and after their rupture in the Fallopian tubes, he traced the changes it un derwent in the first days after copulation, and established satisfactorily the identity of this body with the ova found by previous observers in the Fallopian tubes and cornua of the uterus; thus proving by actual observation what had before been held only from analogy, that in the mammiferous or truly viviparous, as well as in the oviparous animal, the foetus derives its origin from an ovum already formed iu the ovary before fecundation4 Some time after sexual union the fluid con tained in the vesicles which are about to burst, previously transparent and nearly colourless, now becomes more viscid and tenacious, some what turbid and of a reddish colour ; and in some animals it is possible in such ripe vesicles to perceive, with the unassisted eye in a favour able light, a whitish opaque spot on the most prominent part, indicating the layer of granules or proligcrous disc, in the centre of which the ovum is situated. After a certain time a small opening is formed at the most prominent part of the coverings of the vesicle, the vesicle bursts, and its contents escape through the opening ; they are received in the infundibulum, which is now applied firmly against the ovary ; and the ovum entering the Fallopian tube is conveyed along it, probably by its slow and gradual ver micular contractions, until it at last arrives in the uterus.