In a former part of this essay it was remarked that rupture of the Graafian vesicles and dis charge of the ovula from them, as well as the formation of corpora lutea, may take place in some animals without the concurrence of the male : there is reason to believe that in some cases the decidua may in part be formed with out conception having occurred, as in the cases of moles, &c. When these changes have oc curred without conception in Mammalia, it is quite possible that the ova may have been car ried down the Fallopian tubes ; but as they are unfecundated, they undergo no enlargement, and consequently we do not know what be comes of them.
In many oviparous animals the same is the case, that is, ova are frequently discharged from the ovaries without the concurrence of the male, as happens in the common fowl and other birds, in some reptiles and fishes. But even in those animals in which barren ova are thus excreted by the female, union with the male renders the exclusion of the egg more easy and regular, and it is consequently not uncommon for female oviparous animals which are removed from the males to die at the season of breeding, when the ova are formed in their ovaries or de scend from that organ into the oviduct. This is beautifully described by lIarvey as befalling his lady's parrot, which he had always taken for a male bird, but which, after being much fondled, died of " a corrupted egg impacted in the oviduct ;" and also in a cassowary kept in the royal gardens, which, after being some time there, was excited by being placed in the vicinity of a male and female ostrich, and having laid one egg, died of a second being re tained in the oviduct.
In the common fowl indeed, when highly fed, so great is the productive energy both of the ovary and oviduct that they will continue to lay eggs during a whole season without the assistance of the male ; but this is well known to be often very pernicious to the bird, as many of those kept without the cock die ; and it not unfrequently happens that eggs, or bodies like eggs, are laid by them containing no yolk, but consisting only of the albumen, membrane, and shell, which are the product of secretion from the oviduct, and that in others large masses of imperfectly formed eggs accumulated together are lodged in the genital passages.
These facts exhibit in a strong point of view the powerful productive energies of the female generative organs independently of the concur rence of the male ; for it is sufficiently obvious from them that the greater part of the substance of the egg is due to the female, and that ova, to all appearance perfect,• though unfit for repro duction, may be brought forth by the female wholly independent of the male. Some authors
also adduce as examples of this independent productive energy of the female, the occurrence of bones, hair, teeth, &c., in close cysts of the ovaries of women and female quadrupeds, but this leads us too far into the regions of vague supposition.
Irregularities in the descent of the ovum.— This appears to be the proper place at which to make mention of a few irregularities that have been observed in the descent of the ovum, which are attended with important modifica tions of the generative process.
In the bird it not unfrequently happens that the yolk or ovulum which has been discharged from its burst capsule in the ovary, instead of descending through the oviduct, and having added to it the external accessory parts, escapes from the infundibulum or oviduct into the cavity of the peritoneum. This irregu larity occurs most frequently among those fowls which are laying eggs without the male, and in which it may be supposed the usual and regular performance of the appro priate motions is not ensured by venereal ex citement. These yolks sometimes remain for some time in the cavity of the abdomen, and are afterwards gradually removed by absorption : in other instances they cause death. Upon every occasion when the ovulum is discharged from an ovarian capsule, the oviduct is excited to the secretion of albumen, membrane, and shell, and hence the ova subventanea, which consist only of these accessory parts without the yolk.
In other instances, either from a mechanical obstruction to the passage of the egg, or from a deficiency in the muscular power of the oviduct, the product becomes impacted in the passage, and there are formed large masses of accumu lated ova subventanea, with or without yolks in some part of the oviduct or in its vicinity.
In some instances, extremely rarely met with, it is stated by Geoffroy St. Hilaire (Annal. du Museum d'Hist. Naturelle) that ova de tained in the oviduct have become slightly de veloped, and the author owes to the kind ness of his friend, Mr. Daniel Ellis, the his tory of several examples of the same ano maly ; but it may be stated as a general rule that this does not occur in oviparous animals, and more especially in birds, in which a con tinued supply of fresh air around the shell is necessary to promote incubation, and we do not know of any examples of truly oviparous animals in which the fwtus has been formed in an egg accidentally retained within the body of the parent. In none of those which we have observed was there any appearance of fatal formation.