VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 257 



appear to have a limited portion of the middle stage of life allotted for that 

 purpose; it becomes a question, whether those organs are worn out by repeated 

 acts of propagation ; or whether there is not a natural and constitutional period 

 to that power on their part, even if such power has never been exerted ? If we 

 consider this subject in every view, taking the human species as an example, we 

 shall discover that circumstances, either local or constitutional, may be capable 

 of extinguishing in the female the faculty of propagation. Thus we may 

 observe when a woman begins to breed at an early period, as at 15, and has her 

 children fast, that she seldom breeds longer than the age of 30 or 35 ; therefore 

 we may suppose, either that the parts are then worn out, or that the breeding 

 constitution is over. If a woman begins later, as at 2,0 or 25, she may con- 

 tinue to breed to the age of 40 or more ; and there are, now and then, instances 

 of women, who, not having conceived before, have had children as late in life 

 as at 50 years or upwards. After that, few women breed, even if they should 

 not have bred before : therefore there must be a natural period to the power of 

 conception. A similar stop to propagation may likewise take place in many 

 other classes of animals, probably in the female of every class, the period vary- 

 ing according to circumstances ; but still we are not enabled to determine how 

 far it depends on any particular property of the constitution, or of the ovarium 

 alone. 



As the female of most classes of animals has 2 ovaria, I imagined, that by 

 removing one it might be possible to determine how far their actions were re- 

 ciprocally influenced by each other, from the changes which by comparison 

 might be observed to take place, either by the breeding period being shortened, 

 or perhaps, in those animals whose nature it is to bring forth more than one at a 

 time, by the number produced at each birth being diminished. 



There are 2 views in which this subject may be considered. The first, that 

 the ovarium, when properly employed, may be a body determined and unalter- 

 able respecting the number of young to be produced. In that case we can 

 readily imagine, that when one ovarium is removed, the other may produce its 

 determined number in 2 difl^erent ways ; one when the remaining ovarium, not 

 influenced by the loss of the other, will produce its allotted number, and in the 

 same time ; the other, when it is affected by the loss, yet the constitution de- 

 mands the same number of young each time of breeding, as if there were still 2 

 ovaria ; consequently it furnishes double the number it would have been required 

 to supply had both been allowed to remain, but must cease from the perform- 

 ance of its function in half the time. The 2d view of the subject is by sup- 

 posing that there is not originally any fixed number which the ovarium must 

 produce ; but that the number is increased or diminished according to circum- 

 stances ; that it is rather the constitution at large that determines the number ; 



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