146 P. L. Krohn 



menstruating at rather irregular intervals in 1954. Whether 

 it is ovulating or not is unknown.) Another baboon also 

 menstruated over a period of at least fourteen years. A mon- 

 key in the Birmingham colony accidentally died during preg- 

 nancy at an age of fourteen to fifteen, and other spayed 

 animals which are being used to compare the sensitivity to 

 hormones of the uterus in youth and old age are now approxi- 

 mately twenty years old. The only other information is 

 provided by Hartman (1938) who mentions that his colony 

 of rhesus monkeys contained two animals which reached the 

 ages of eighteen and seventeen before they died. Both were 

 still menstruating but they had not ovulated for the preceding 

 three and one-and-a-half years respectively. Since the 

 menarche occurs at about the age of four, these fragmentary 

 observations suggest that reproductive life in monkeys may 

 last for as long as twenty years, a period which probably 

 represents a greater proportion of the total lifespan than does 

 the phase of reproductive life in women. 



Strain differences in the rate of changes w^ith age 



The rate at which reproductive function comes to an end 

 seems to vary considerably even within a single species. 

 Fekete (1953) has described the histological appearance of 

 the ovaries of different aged mice from eight inbred strains. 

 Her observations are only qualitative but they show, for 

 instance, that the number of follicles is noticeably diminishing 

 in mice of the RIII and C57 strains when they have reached 

 the age of eight months, while similar changes have not taken 

 place in the C3H strain at thirteen months of age. Loeb (1948) 

 also provides qualitative information about inter-strain 

 differences in the number of follicles and in the histological 

 appearance of other components of the ovaries of mice. 



Some similar observations have been reported by Wolfe 

 and Wright (1943) for two strains of rats, which, at equal 

 ages, differed not only in the relative proportions of the cell 

 types in the pituitary but also in the numbers of normal and 

 atretic follicles and of corpora lutea. However, Wolfe and 



