From this it results that the ovary in Man, as well as in the Mammalia generally, has three noticeable periods : the first, of prepara tion ; the second, of activity ; and the third, of decay : and these correspond respectively with the periods of infancy and childhood, of youth and prime, and of decline and old age.
The condition of the ovary at each of these epochs will be traced ; but the middle period is obviously that to which the chief interest attach es.
During certain portions of this epoch, and in some instances through more or less of its whole extent, the ovary is employed in ripen ing and cmitting ova. In this respect, how ever, greater variation is perceptible in dif ferent species than in any other particular. But in all alike this one circumstance is ob servable, namely, that the emission of ova is a periodic occurrence.
Now the periods of emission of ova may so occur as to make the times of parturition co incident with the returns of those seasons which are most favourable for the rearing of the young. In such cases the capacity for impregnation may be limited to one period of the y ear, the ova being ripened and emitted only at that time. The roe affords an inter esting example of this. The doubts which have been sometimes entertained as to the precise time at which the roe becomes impreg nated have now been settled by the recent very careful researches of Bischoff*, who has proved that this occurs at the end of July and during the month of August, and that it is only then that the ovaries of the female con tain ripe ova, and the testes of the male ripe semen. At other times these are not to be found ; hence it follows that in this animal im pregnation is impossible at all other seasons.
But in many animals the periods of ripening and discharge of the ova recur with much greater frequency ; and probably- climate, food, domestic care and the like, exercise a certain degree of influence in modifying the returns of these periods.
In the human female the same periodicity is observable; and it is now rendered in the high est degree probable that in her case the times of ripening and generally of the discharge of the ova are coincident with the times of menstruation*, just as it has been proved beyond dispute that in other Mannualia the same process accompanies that more obvious condition of aptitude and desire for sexual intercourse to which the terms cestrus and rut are applied.
A periodical maturation, therefore, of ova, accompanied by dehiscence of the ovicapsules and discharge of their contents, may be said to constitute the principal offices of the ovary during the prime of life. But notwithstanding that these processes are periodicallyperformed, the ovary cannot at any time be said to be in a condition of perfect rest, except under cir cumstances which will be presently noted; for whilst some ovisacs may be observed to be advancing and preparing to emit ova, others may be seen receding or becoming obliterated. The climax, however, of each serial process is the dehiscence or rupture of one or more follicles. Upon this the whole force of the ovary is, as it were, for the time concentrated. This event being terminated, the activity of the ovary passes away as regards that parti cular follicle. Enough, however, of vital energy remains in the now useless part to suf fice for the healing of the wound, and the closing and obliteration of the cavity left after the escape of the ovum. But the blood gra dually deserts the walls of the previously congested ovi.ac, the distended vessels in its neighbourhood shrink and become obliterated, and the action is transferred to another set of follicles, one or more of which pass through a similar order of changes.
Two circumstances, however, arrest for a time this process. The one is the occurrence of utero-gestation, the other the performance of lactation ; and although occasional excep tions may be observed, yet so far as this ques tion has been examined, the evidence collected favours the belief, that in pregnant women and in those who suckle, no ova are emitted during the continuance of either of these processes.1 This view also, so far as relates to lactation, receives support from the well-known circum stance that a considerable degree of immunity from impregnation occurs during the conti nuance of lactation, a circumstance easily ex plained upon the supposition that at that time usually no ova are matured or emitted.