80 
JOURNAL OF MAMMALOGY 
presumably ‘‘naturaF’ death at a date which was unfortunately not 
recorded. This mouse is known, however, to have reached an age of 
at least 3 years and 2 months. 
The remaining seven individuals died at the following.ages: 
9 71 3 years, 0 months 
0^20 ....3 “ 4(+) “ 
9 11 4 “ 2 “ 
d’ 39 4 “ 5 
9 81 4 “ 8(+) 
9 2 5 “ 3 (-) “ 
9 22 5 “ 8 (-) 
Thus, five of these mice attained an age of more than four years, 
while two attained an age of more than five years. The patriarch 
(or rather, matriarch) among them reached the ripe age of 5 years and 
8 months. 
In all of these seven cases, death resulted from disease or ‘^old age.’^ 
Several of the mice became extremely senile and “wobbly'^ long before 
death occurred, and it was noted that several of them were very much 
affected by cold. Such individuals became numb and feeble on cold 
days, and it is perhaps significant that five of the deaths occurred 
during the winter or late fall. 
No obvious changes occurred in the appearance of the senile pelages, 
though the two oldest of these have been saved for more careful study. 
It is worth noting that of the two which died in the sixth year one was 
dark and the other somewhat buff, representing the normal range of 
variation in adult individuals of this subspecies. It was noticed that 
one of the males, in middle or late life, acquired a curious ‘‘grizzled^^ 
appearance in the hair of the face, giving him a decidedly venerable 
appearance. I found, however, that this was a hereditary peculiarity 
of the family to which the grizzled mouse belonged. It was noted in 
at least four other individuals, in some cases while the animals were still 
young. 
Unfortunately, my records, as regards the fertility of this ‘^old age’^ 
stock, are very meagre. At the commencement of the experiment, 
all were mated, except one male, which was kept apart until he was 
nearly three years old, and then mated. No record was kept of the 
earlier broods resulting from these matings. It is probable that some 
of the individuals were sterile from the outset, a condition not infre- 
quent among cage-bred Peromyscus. 
