724 GEXEKATIOX AKD DEVELOPMENT. 



vesicle are liberated, and escape on the exterior of the 

 ovary, whence they pass into the Fallopian tube, the fim- 

 briated 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 appear 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 impregnation by the male, or even 

 of sexual union. And it is now established 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 by 

 the phenomena of menstruation. Sexual desire manifests 

 itself in the human female to a greater degree at these 

 periods, and in the female of mammiferous animals at no 

 other time. 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 Mam- 

 malia, 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 



