GENERATION. 



451 



followed simple excitement of the sexual 

 organs, and might therefore take place either 

 with or without the male ; and in the second 

 place, the occurrence of cavities and vesicular 

 membranes within the corpora lutea is by no 

 means a proof that these cavities are new or 

 forming ovarian vesicles ; on the contrary, there 

 is every reason to regard them as unnatural or 

 the product of disease. But though lately 

 revived upon the above-mentioned grounds, it 

 is long since this hypothesis received the most 

 satisfactory refutation, both from the observa- 

 tions of De Graaf and of Haller. Haller in 

 particular traced in the most accurate manner 

 all the steps of the development of the corpus 

 luteum, from the first rupture of the vesicle 

 till its completion : he employed the animals 

 least liable to lead to fallacy in such observa- 

 tions ; those, viz. in which rupture of the 

 vesicles and formation of corpora lutea is 

 usually produced only by sexual union ; and 

 he always remarked in them an exact corres- 

 pondence in the number of foetuses in the 

 gravid uterus with the number of corpora lutea 

 in the ovaries, while at the same time he found 

 the first appearance of these bodies to take 

 place at a fixed period after sexual union, and 

 their size and structure always to bear an exact 

 relation to the period of utero-gestation at 

 which they were observed.* 



The uses of the corpora lutea are entirely 

 unknown. The fact that these bodies become 

 larger and remain proportionately of a larger 

 size during pregnancy than when produced in 

 other circumstances (as without sexual union, 

 or after unproductive copulation, or when the 

 product is blighted at an early period of utero- 

 gestation,) would seem to indicate some con- 

 nexion between the corpora lutea and the 

 development of the foetus in utero. By those 

 who have regarded the corpora lutea as of a 

 glandular nature, they have been supposed to 

 secrete fluids which assist in the nourishment 

 of the foetus. We have already stated the 

 reasons for considering such hypotheses as 

 groundless. (See OVARY.) 



Descent of the ovum. Its structure and 

 changes during its passage. The attention of 

 accoucheurs in all ages and countries has 

 naturally been directed to the study of the 

 structure of the human ovum and foetus in the 

 more advanced stages of utero-gestation, and 

 a great body of facts has been collected from 

 the examination of aborted products or the 

 gravid uterus of women dying during preg- 

 nancy, from which scientific men have acquired 

 an accurate knowledge of the structure of the 

 human foetus and its covering in the ovum 

 during the greater part, and especially in the 

 more advanced period of utero-gestation ; but 

 very little is known of the nature of the egg 

 in the first stages or immediately after concep- 



* The corpus luteum is developed then and be- 

 comes perceptible after the bursting of one of the 

 vesicles , but let us not here lose sight of the fact 

 before announced that the first commencement of 

 its formation dates from a short while before the 

 rupture, as indicated by a thickening of the inner 

 membrane of the vesicle. 



tion has occurred. We hare, in feet, no direct 

 observations which inform us of what happens 

 to the human ovum immediately after its escape 

 from the ovary, and, indeed, for some little 

 time after its arrival in the uterus, when the 

 parts of the foetus have already begun to be 

 formed in it. This subject has, however, been 

 investigated with considerable success in several 

 mammiferous animals ; and although there 

 remain several points which still require eluci- 

 dation, yet, from the analogy which is known to 

 exist in the structure of the ovum and foetus 

 of the human species and those of quadrupeds 

 and birds, we are enabled to bring together the 

 detached observations which chance has thrown 

 in our way, and thus to give a connected 

 account of the generative process in man, im- 

 perfectly as that process has as yet been 

 observed. 



Our design at present is to follow the ovum 

 only as far as into the uterus, or until the com- 

 mencement of the formation of the foetus in it. 

 We believe we shall place this part of our sub- 

 ject in the clearest point of view, by prefixing 

 to our remarks regarding the ovum of man 

 and quadrupeds a short sketch of what happens 

 to the egg of the common fowl after its dis- 

 charge from the ovary. 



The substance of the yolk enclosed in its 

 membrane, together with the germinal portion 

 in which after incubation the rudiments of the 

 new animal begin to be formed, constitutes the 

 essential parts of the bird's egg as it exists in 

 the ovary. The ovarian egg, when it has left 

 the place of its formation and passed into the 

 oviduct, receives the addition of various other 

 parts, viz. the albumen, chalazae, shell and 

 its lining membrane, as it gradually descends 

 through different portions of the oviduct, each 

 of which is destined to secrete one of these 

 newly added parts. These parts may, however, 

 be considered as accessory to the more essential 

 constituents of the egg, which we are inclined 

 to regard as the germinal spot or cicatricula, 

 the granular and oleaginous fluid of the yolk, 

 and the dense transparent membrane with 

 which they are enveloped. To the unim- 

 pregnated egg of the ovary we shall give the 

 name of ovulum, and henceforward in this 

 paper apply the name of ovum to the perfected 

 egg, that is, the ovulum to which the acces- 

 sory coverings have been added, and which 

 has received! the influence of the male. The 

 ovarium of the common fowl in the breeding 

 season, or when it is laying eggs, has the form 

 of a bunch of clustering ovula, which are 

 contained in capsules, the more advanced of 

 which hang down from the rest of the ovary 

 by the elongated pedicles of the containing 

 capsules ; while the smaller ovula of various 

 sizes, composing the body of the ovary, cluster 

 more closely together. The fully developed 

 ovula only have the deep yellow colour pecu- 

 liar to the yolk ; as the smaller ones are less 

 advanced their colour is paler, and the smallest 

 are nearly colourless and transparent from 

 the absence in them of the oleaginous and 

 granular matter peculiar to the riper yolks. 



The little white spot or granular layer which 



