GENERATION. 



449 



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 proligerous 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. 



With regard to the time at which the opening 

 of the ovarian vesicles takes place, there are 

 considerable varieties in the same and in diffe- 

 rent animals. In the sheep, the vesicle has 

 been found burst so early as at two hours after 

 coition. In the dog, Haller found the vesicles 

 burst before the sixth day ; in one instance the 

 day after coition ; but Prevost and Dumas, not 

 until the seventh or eighth. In the rabbit, 

 Cruikshank observed vesicles burst two hours 

 after coition, while Haighton considers forty- 

 eight hours as the usual time at which the rup- 

 ture happens in this animal. M. Coste has 

 observed it most frequently between the second 

 and third day in the rabbit. 



After the bursting of the Graafian vesicles, 

 there occur in them and in the neighbouring 

 part of the ovary some important changes of 

 structure, which claim our attention in this 

 place as intimately connected with that part of 

 the process of conception which is now under 

 consideration. 



If the Graafian vesicle which is enlarged 

 from venereal excitement and is ready to burst, 

 be examined with care, it will be seen that at 

 the most prominent part of its coats the blood- 

 vessels converge towards the point at which 



rupeds, (Annal. d. Scien. Nat. torn. iii. p. 135,) 

 but without any certainty or exact knowledge as to 

 their nature. M. Coste, with a spirit of appropria- 

 tion too common, we regret to say, among his coun- 

 trymen, has taken advantage of some speculative 

 views and strained analogies brought forward by 

 Baer concerning the bodies which he discovered, in 

 which he compared them (erroneously as we think) 

 to the germinal part only of the ovum, rather than 

 to the whole ovum of the oviparous animal, to take 

 from the merits of Baer in their discovery ; but we 

 feel assured that every unprejudiced inquirer who 

 reads with attention Baer's admirable " Epistola 

 de Ovi Mammalium et Hominis Genesi," in which 

 his discovery was first announced in 1827, and 

 compares it with other works on the subject, 

 will be convinced that Baer has no sharer in the 

 discovery, and fully understood the nature of the 

 ovarian ovum of viviparous animals ; although 

 it t may be the case that subsequent investigations 

 have added considerably to the knowledge of the 

 relations of these ova. We shall return to a more 

 minute detail of this body in considering the process 

 of formation of the ovum in the present article and 

 under the article OVUM. 



the rupture afterwards takes place, and this 

 point is itself comparatively destitute of blood- 

 vessels.* 



At the time of the formation of the opening 

 into the vesicle, from the division of some of 

 the bloodvessels, a small quantity of blood is 

 generally mixed with the fluid contents of the 

 vesicle ; and after the vesicle has been emptied 

 of these fluid contents, their place is generally 

 supplied by a greater or less quantity of coagu- 

 lated blood, probably poured out by the same 

 ruptured vessels. 



The membranes of the vesicle at this time 

 have become thicker than before : the inner 

 one in particular appears more vascular and 

 uneven, perhaps in part from its being puckered 

 up on the vesicle becoming flaccid and com- 

 paratively empty. The wrinkled appearance 

 on the inner surface of the vesicle increases, 

 and there grows gradually out from it a new 

 substance which comes to occupy the whole 

 cavity of the vesicle ; and in many instances, 

 as this new substance is formed in greater 

 quantity than can be contained within the limits 

 of the vesicle, it protrudes some way out at 

 the opening of the vesicle, forming a dark red 

 prominence like a nipple, which rises above 

 the neighbouring surface of the ovary. This 

 substance, at the time of its first formation, is 

 of a pink or reddish colour, but as it becomes 

 gradually less filled with blood it acquires a 

 yellowish hue, which is more or less apparent 

 in different animals. In the human species it 

 is of a bright yellow colour, whence the name 

 of corpus luteum applied to this new produc- 

 tion of the ovarian vesicles. 



The substance of the corpus luteum has a 

 lobular structure ; the lobules radiating in a 

 somewhat irregular manner from the centre to 

 the circumference. The central part of the 

 corpus luteum frequently remains hollow for 

 some time after its production, opening ex- 

 teriorly by a narrow passage from the place 

 where the rupture of the vesicle originally took 

 place ; at other times this passage is closed 

 more early, and there remains nothing but an 

 indication of its place in a depression in the 

 centre of the most projecting part of the corpus 

 luteum. The lobules of the corpus luteum, 

 examined with the microscope, exhibit merely 

 a granular structure, and are not formed of 

 acini, as some have described them, so that 

 there is no reason to consider these bodies as 

 of a glandular nature. 



The size which corpora lutea attain when 

 fully developed varies much in the same and 

 in different animals. In the human female 

 they become as large as a common hazel-nut ; in 

 the cow they are sometimes as large as a ches- 



* The ovarian capsules of the bird, which are 

 obviously the analogous parts of the ovarian 

 vesicles of quadrupeds, present on their most pro- 

 minent part a remarkable band, extending for 

 nearly one-third of the periphery : towards the 

 margins of this band the small bloodvessels all 

 converge, but they do not pass upon the band 

 itself, so that it is left free from bloodvessels. It 

 is in this non-vascular or less vascular part of the 

 capsule that the rupture takes place when the yolk 

 escapes. 



