SETON — BREEDING OP DEERMICE 
137 
li^ke old ones and scrambling over the bars of the cage. On July 18 
(40 days old), they were completely weaned and nearly full grown. 
June 6. To-day saw signs of rut in the old pair of deermice. In 
thirteen days the female was well advanced in pregnancy. On June 22, 
the 16th day, she was found with 4 new-born young tight on her teats; 
3 on the inguinal, 1 on the pectoral; which may mean that I was 
wrong about the mating time. On the 16th day after birth, their eyes 
are fully opened, and they are very active. 
These mice are extremely fond of nuts and can quickly get at the 
meat of a shellbark. But when given choice, they went first for some 
acorns and finished them, before touching the hickories. They killed 
and devoured a cicada that was put with them. 
Fig. 3. Mammje op Peeomyscus letjcopus. 
Two-thirds natural size. 
At another time I had but one deermouse in the cage when a meadow- 
mouse {Microtus) arrived and was put in to keep him company. I 
watched closely fearing that they might fight, in which case I expected 
it would be necessary to rescue the deermouse. But it turned out other- 
wise. 
The deermouse made one or two darts of bewildering quickness, 
and the meadowmouse beat a retreat. Within two days they were 
good friends, and made a joint nest in a curl of birch bark. Though 
much more intelligent than his friend, the deermouse had made little 
effort to escape from the cage, but the meadowmouse spent most of his 
time gnawing at the wooden parts of the frame. In particular he worked 
at the upper part where he had to cling and gnaw at the same time. 
