PHASES IN THE LIFE OF THE INDIVIDUAL 717 



Other changes, depending ])robalily on the degenoration of the 

 ovaries, are the assumption of certain of the secondary male 

 characters. These are apparently more marked in some animals 

 than they are in the human species, and have already been men- 

 tioned in dealing with the internal ovarian secretions (\>. .'J40). 



The ages at whicii domestic animals cease to breed have lieen 

 only imperfectly determined since they generally die liofore reaching 

 their climacteric. Mares have l)een known to produce young beyond 

 thirty years,i shee[) up to twenty, and cats to fourteen, luit they may 



Fig. 184. — Section through uteiine mucous meuibiuiie of woman of 

 sixty. (From Sellheim.) <jl, Glands. 



cease somewhat earlier and yet maintain a healthy existence for a 

 few years.^ Kirkham-* says the white mouse stops reproducing at 

 eighteen to twenty-two months after having twelve to sixteen litters. 

 The menopause in the white rat occurs at the age of fifteen to 

 eighteen months.* 



' Wood (W. A.) found that out of 1216 thoroughbred mares recorded in 

 the earlier volumes of the General Stnd-hool; one bred at 33, two at 30, four 

 at 29, seven at 28, and seventeen at 27. He draws the conclusion that in actual 

 practice the mare generally continues to bleed as long as she lives ("Note on 

 the Breeding Age of Thoroughbred Mares," Vet. Jour., December 1921). 



- Fleming, Veterinary Obstetries, 3i'd Edition, by Craig, London, 1912. 



^ Kirkham, loc. eit. 



^ Donaldson, Ive. eit. 



