450 



GENERATION. 



nut ; and in the sow or ewe they are somewhat 

 larger than full-grown peas. 



The corpus luteum may, by dissection, be 

 easily separated from the surrounding parts and 

 turned out of the ovary ; and when this is 

 done, the external membrane of the original 

 vesicle remains lining the cavity left in the 

 ovary. From this it would appear that the 

 corpus luteum is most intimately connected 

 with the inner membrane of the vesicle ; and, 

 in fact, Baer* observed that, before the rupture 

 of the vesicle in the dog, the inner membrane 

 had become thickened, rugous, and of a villous 

 structure, as if the corpus luteum grew from 

 that internal membrane itself. This observa- 

 tion also makes it probable that the growth of 

 the corpus luteum may contribute to cause the 

 rupture of the vesicle. 



The corpus luteum at first increases gradu- 

 ally in size, remains for a time stationary, and 

 then decreases till it either wholly disappears 

 or leaves only a small mark or cicatrix to indi- 

 cate its place. The time at which it attains 

 its full size seems to vary considerably. In 

 the sheep two or three days are sufficient for 

 the formation of the corpus luteum, and its 

 cavity becomes obliterated within a fortnight 

 after copulation. Haller found corpora lutea 

 in the dog on the sixth day; Cruikshank 

 observed the corpora lutea to go on progres- 

 sively increasing till the ninth day in the 

 rabbit; and it is probable that in the human 

 species the corpus luteum is not fully developed 

 till after the second month of pregnancy. 



After the corpus luteum has attained its full 

 magnitude, its colour becomes paler and of a 

 clearer yellow; its size then gradually dimi- 

 nishes, its tissue becomes more compact, its 

 cavity is obliterated, and it is converted into a 

 body nearly solid. It generally retains, during 

 utero-gestation, a considerable size, and this 

 remark applies especially to the human species, 

 in which it diminishes much more rapidly in 

 size after than before the birth of the child. In 

 some animals it at last wholly disappears ; in 

 others, among which is the human species, it 

 always leaves some mark. 



In what has now been said regarding the 

 corpus lureum, that body has been described 

 as it is formed in the place of a vesicle which 

 has been burst after fruitful sexual union ; but 

 we may remark that the same series of changes 

 always follows the rupture of an ovarian 

 vesicle from whatever cause that may have 

 proceeded. It is now well known that in 

 some animals the rupture of ovarian vesicles 

 and subsequent changes take place without 

 sexual union merely from the state of heat or 

 venereal excitement of any kind, while in 

 others these phenomena are never observed 

 but as accompaniments of conception. The 

 sow and mare belong to the first of these classes 

 of animals. The rabbit, bitch, ewe, and cow 

 may be mentioned as examples of the second, as 

 also is generally the case in the human female ; 

 but in woman, as in some other females, various 

 circumstances induce us to believe that the 



* See Epistola, &c. 



rupture of ovarian vesicles and the formation 

 of corpora lutea in their place occasionally 

 happen without sexual union from all those 

 causes which excite greatly the sexual organs ; 

 and we are not, therefore, inclined to admit 

 the presence of a corpus luteum, . taken alone, 

 as a certain sign of sexual union having oc- 

 curred ; though conjoined with other signs, the 

 presence of one or more corpora lutea or the 

 appearance of ruptured vesicles must be re- 

 garded as good presumptive evidence. 



In some of those animals in which vesicles 

 frequently burst without sexual union, there 

 are occasionally very many corpora lutea in 

 the ovary, so as to alter completely its form, and 

 disguise its natural structure, as may frequently 

 be seen in the sow. In those animals again 

 in which sexual union alone brings about the 

 rupture, we at once distinguish the ovary of 

 the unimpregnated animal from that of the one 

 that has had connexion with the male, and we 

 very generally observe an exact correspondence 

 in the number of corpora lutea and the ova or 

 foetuses contained in the uterus;* and the 

 same correspondence is very frequently found 

 after conception, even in those animals in which 

 corpora lutea are formed without sexual union. 



While the corpus luteum, then, is always to 

 be found in the ovary of a pregnant quadruped, 

 the formation of this body is to be regarded as 

 the uniform consequence of the rupture of the 

 ovarian vesicles, whether thai rupture shall 

 have been occasioned merely by excitement of 

 the organs, or by productive or unproductive 

 sexual union ; but it is only when conception 

 and pregnancy occur that the corpus luteum 

 attains its full size, and runs through the whole 

 of that series of changes which we have described 

 as peculiar to that body. 



We ought not to omit here the mention of a 

 totally different view which has been taken of 

 the corpora lutea, that, viz. of Buffon and Val- 

 lisneri,f supported more recently by Sir E. 

 Home,J according to which it is held that the 

 corpora lutea exist before the rupture of the 

 vesicles, and are the matrix in which the vesicles 

 and ova are formed. 



Two circumstances principally have been 

 brought forward in favour of this hypothesis : 

 1st, that corpora lutea occur in the virgin state; 

 and 2d, that they frequently contain vesicles. 

 Now the existence of corpora lutea, we have 

 already stated, in the sow (observed by Sir E. 

 Home;, and even, we are inclined to hold, in 

 the human female, is not necessarily a proof 

 of sexual union having previously occurred, 

 since the rupture of the vesicles may have 



* It may be mentioned that more than one ovum 

 have sometimes been found in the same Graafiaii 

 vesicle, in which case it will readily be understood 

 there might be only one corpus luteum in the ovary 

 and two ova in the uterus, but this is rare. The 

 author has verified the above correspondence in 

 many hundred pregnant ewes, in a considerable 

 number of cows, rabbits, some cats, and other 

 animals. 



t Vallisneri, Hist, of the Generation of Man and 

 Animals (Ital.). 



$ Phil. Trans., vol. cviii. p. 256, and vol. cix. 

 p. 59. 



