GENERATION. 



455 



furnishes a soft flaky lining to the cavity of the 

 uterus, and serves to form a covering of the 

 ovum when it afterwards descends into the 

 uterus. This newly formed substance is re- 

 flected over the ovum so as to give it a double 

 covering, the two layers of which constitute the 

 two folds of the decidual membrane. The 

 decidua is filled with bloodvessels formed by 

 a process of organization similar to that which 

 occurs in inflammatory adhesion by coagu- 

 lable lymph. These bloodvessels are conti- 

 nuous with those of the uterus, and as the 

 ovum advances in the progress of develop- 

 ment, they are much dilated in some parts 

 so as to form sinuses, which are ultimately 

 intermingled, though by no means continuous 

 with the bloodvessels which pass out of the 

 umbilicus of the foetus. The placenta or or- 

 ganic connection between the female parent 

 and child, by means of which the respiration 

 and partly also the nutrition of the latter is car- 

 ried on, is in great part formed in the decidua 

 with which the flocculent chorion is closely in- 

 corporated ; but the description of these parts 

 belongs to another place. 



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 Harvey 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 Geoffrey 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- 



* We shall have occasion to consider elsewhere 

 more minutely the difference between the lecun- 

 dated and the unfecundated ovum. 



