240 HAND-BOOK OF PHYSIOLOGY. 



with the increase of size, caused by the augmentation of its liquid con- 

 tents, the external envelope of the distended vesicle becomes very thin and 

 eventually bursts. By this means, the ovum and fluid contents of the 

 Graafian vesicle are liberated, and escape on the exterior of the ovary, 

 whence they pass into the Fallopian tube, the fimbriated processes of the 

 extremity of which are supposed coincidentally to grasp the ovary, while 

 the aperture of the tube is applied to the part corresponding to the 

 matured and bursting vesicle. 



In animals whose capability of being impregnated occurs at regular 

 periods, as in the human subject, and most Mammalia, the Graafian 

 vesicles and their contained ova appear to arrive at maturity, and the 

 latter to be discharged at such periods only. But in other animals, e.g., 

 the common fowl, the formation, maturation, and discharge of ova ap- 

 pear to take place almost constantly. 



It has long been known, that in the so-called oviparous animals, 

 the separation of ova from the ovary may take place independently of im- 

 pregnation by the male, or even of sexual union. And it is now estab- 

 lished that a like maturation and discharge of ova, independently of 

 coition, occurs in Mammalia, the periods at which the matured ova are 

 separated from the ovaries and received into the Fallopian tubes being 

 indicated in the lower Mammalia by the phenomena of heat or rut: in the 

 human female, although not always with exact coincidence, by the phe- 

 nomena of menstruation. If the union of the sexes take place, the ovum 

 may be fecundated, and if no union occur it perishes. 



That this maturation and discharge occur periodically, and only during 

 the phenomena of heat in the lower Mammalia, is made probable by the 

 facts that, in all instances in. which Graafian vesicles have been found 

 presenting the appearance of recent rupture, the animals were at the time, 

 or had recently been, in heat; that on the other hand, there is no authentic 

 and detailed account of Graafian vesicles being found ruptured in the 

 intervals of the period of heat; and that female animals do not admit the 

 males, and never become impregnated, except at those periods. 



Menstruation. Many circumstances make it certain that the human 

 female is subject, in these respects, to the same law as the females of 

 other mammiferous animals; namely, that in her as in them, ova are 

 matured and discharged from the ovary independent of sexual union. 

 This maturation and discharge occur, moreover, periodically at or about 

 the epochs of menstruation. Thus Graafian vesicles recently ruptured 

 have been frequently seen in ovaries of virgins or women who could not 

 have been recently impregnated; and although it is true that the ova dis- 

 charged under these circumstances have rarely been discovered in the 

 Fallopian tube, partly on account of their minute size, and partly because 

 the search has seldom been prosecuted with much care, yet analogy for- 

 bids us to doubt that in the human female, as in the domestic quadrupeds, 



