450 OP GENERATION AND DEVELOPMENT. 



not confined to the Human female, as was formerly supposed; but 

 occurs in some of the lower Mammalia in the state of heat, or periodi- 

 cal aptitude for procreation, at which time the ovarium contains ova 

 ready for impregnation. The chief peculiarity attending its appearance 

 in the Human female, is its regular monthly return. In the natural 

 condition of many of the lower Mammalia, as in Oviparous animals, 

 the period of heat recurs at some one time of the year, usually in 

 the spring ; or, in the smaller and more prolific species, from two to 

 six times. And in those which have undergone a change by domesti- 

 cation, the recurrence is usually irregular, depending upon various 

 circumstances of regimen, temperature, &c. The general analogy 

 between the Menstruation of the Human female and the Heat of the 

 lower Mammalia, consisting in the peculiar aptitude for impregnation 

 which then exists in consequence of the maturation of ova in the ovarium, 

 cannot now be questioned ; but it appears that in the Human female 

 ova may be matured and impregnated at any part of the period which 

 elapses between the occurrences of the Catamenial discharge ; though 

 it is certain that the aptitude for conception is much greater, during 

 the few days which precede and follow the menstrual period, than at 

 any intervening time. The duration of the period of aptitude for pro- 

 creation, which is marked by the continued appearance of the Cata- 

 menia, is more limited in Women than in Men ; usually terminating at 

 about the 45th year. It is sometimes prolonged, however, for ten or 

 even fifteen years longer ; but cases are rare, in which women above 50 

 years of age have borne children. There is usually no menstrual flow 

 during pregnancy and lactation ; in fact the cessation of the Cata- 

 menia is usually one of the first signs indicating that conception has 

 taken place. It is by no means uncommon, however, for them to 

 appear once or twice subsequently to Conception ; and their appearance 

 during Lactation, especially if it be much prolonged, is still more fre- 

 quent ; hence it might be inferred, that the continuance of Lactation 

 may not prevent a fresh conception, which is found to be true in 

 practice. 



800. We shall now take a brief survey of the changes which occur 

 in the Ovulum, when it is being prepared for fecundation ; and of the 

 principal features of its subsequent development. Up to the period 

 when the Ovule is nearly brought to maturity, it remains suspended 

 in the centre of the cavity of the Ovisac ; but it then begins to move 

 towards that side of the Graafian follicle, which is nearest the surface 

 of the ovarium. An important change is at the same time occurring 

 in the Graafian follicle itself ; for whilst the part with which the ovule 

 comes in contact gradually thins away, the outer or vascular layer of 

 the remainder, especially on that side most deeply imbedded in the 

 ovary, becomes much increased in thickness; and a great increase 

 takes place at that part, in the cellular layer that lines the ovisac, 

 which presents a reddish glutinous aspect. This subsequently under- 

 goes a still greater augmentation, and becomes more fleshy ; projecting 

 like a mass of granulations from the interior of the ovisac, and 

 receiving blood-vessels which pass into it from the vascular membrane 

 rthat surrounds it. At the same time, the wall of the Graafian follicle 



