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JOURNAL OF MAMMALOGY 
them by force and carry it in her mouth to the nest. (I have also seen 
them in the woods, carrying their young both ways.) One young 
which I measured was, body 2 inches long, tail It was fully haired, 
but eyes not open. 
This same day, I put the father mouse back in the cage with the 
family. He at once ensconced himself in the nest, despite the mother, 
who fought him off a number of times, uttering meanwhile a thin twitter- 
ing. He did not resist but held up his paws whenever she approached. 
When I removed most of the nest, he helped the mother to carry it 
back and pack it around themselves and the young ones. 
June 21. The young still have their eyes tight closed (13th day). 
I examined one out in the sunlight, but saw not the beginning of aper- 
r- r. 
Fig. 2. External Genitals of Peromyscus leucopus noveboracensis. 
Female. 
One and one-half times natural size. 
ture. They are now big and strong, and sometimes wander outside 
the nest. At once mother, never father, carries them back. Never- 
theless, father cuddles them much when in the nest. Often they hang 
onto the mother^s teats, when she comes out. So far it has been always 
the inguinal teats, never the pectoral, that are so used. 
June 28. The young mice have their eyes open to-day (the 15th 
day). They are now about half the dimensions and a quarter the 
weight of the mother. They are very active and climb extremely well. 
I saw the tail of one projecting from the nest and gently lifted him up by 
it. To my surprise I also lifted his mother to whom he was attached 
and his two brothers who were attached to her, all by the inguinal 
teats. On June 26 (18th day) I saw them for the first time running 
