SUMNER — LONGEVITY IN PEROMYSCUS 
81 
My few positive results bearing on the duration of the reproductive 
period are as follows. One pair (92 and cf 21) produced a brood of 
five or six young, when at the age of 31 months. Two of these 
reached the age of 4 months and were then killed. The father met an 
accidental death not long after, and the mother was mated to cf 20, 
whose fertility was unknown. No further broods resulted. 
Another pair (9 81 and d' 39) produced one brood at the age of 
33 months, and another when more than 34 months old. They were 
remated about 5 months after the birth of this last brood, but no 
further young were produced, though these mice lived together for 
more than a year. The two broods referred to contained but two 
individuals each, and of these four only two reached the age of two 
weeks. From these facts and those mentioned in the preceding para- 
graph, it seems possible that the offspring of parents of this age tend 
to be weak. But such sickly broods may be born to parents at any 
time of life, and the results here cited may have no relation to the age 
of the parents. 
Females 2 and 22, when nearly five years old, were mated to a fertile 
male of another lot, but no young resulted, as might have been con- 
fidently expected. 
A record for two other mice of my stock is worth reporting here. 
The pair in question were wild ones, whose age, at the time of trap- 
ping, was of course unknown, though they were probably at least sev- 
eral months old at the time. Their last brood was born very nearly 
three years later. 
The salient facts in the foregoing discussion seem to be that one 
mouse of the subspecies Peromyscus maniculatus gamheli is known to 
have reached the age of five years and eight months in captivity, while 
two pairs are known to have produced young when both parents were 
nearly or quite three years old. 
Scripps Institution, La Jolla, Calif, 
JOUBNAL OF MAMMALOGY, VOL. 3, NO. 2 
