















MAMMALS OF MINNESOTA. 21 
~ retina, which seem to be the seat of the color sense, are absent, 
and it is supposed that all variations of color are translated 
into shades of black and white, so that the world seems to a 
‘bat like a charcoal drawing or steel engraving. The sense of 
hearing is highly, but peculiarly developed. The reader may 
have noticed that the vocal powers of bats are not great, and 
_ that the voice is pitched very high, so high indeed, that, to 
many ears, the tones are indistinguishable. The sense of hear- 
ing is similarly keyed, so that the bat can readily distinguish 
tones which the human ear is not adapted to perceive. Thus 
the hum of an insect which will startle a bat could only be ap- 
preciated by us as weobserve the motion of the wings causing it. 
EXPLANATION OF FIG. 1. 
1. Epomophorus. 3. Cheronycteris. 
2. Pteropus. 4. Phyllorhina. 
V5 5. Megaderma. 6. Chilonycteris. 
The bats of temperate regions pass the winter in caverns and 
deserted buildings, where, collected in vast numbers, they sleep 
during the cold season. The winter’s sleep varies in length 
and soundness with different species. A sort of classification 
may be observed in the myriads of animals which congregate 
in such places, those which ‘are least susceptible to cold being 
found in the more exposed portions, while the more sensitive 
ones are found in securer retreats. Bats congregate in such 
rendezvous from great distances and the period during which 
the scattered tribes are gathering is one of commotion, quar- 
reling and screaming. The sleepy animalsare in a petulant hu- 
‘mor and struggle for the best places so as to be mostaptly com- 
pared to a covey of chickens settling themselves upon their , 
