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 vdice 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 we observe the motion of the wings causing it. 



4. 



EXPLANATION OF FIG. 1. 



1. Epomophorus. 3. Chseronycteris. 



Pteropus. 4. 



lerma. 6. 



Pteropi 

 Megaue 



ny( 



Pbyllorhina. 

 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 fou"nd 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 animals are in a petulant hu- 

 mor and struggle for the best places so as to be most aptly com- 

 pared to a covey of chickens settling themselves upon their 



