270 
The Mammals of Colorado 
difficult for the collector to shoot them. The power of flight 
varies nearly as much in bats as in birds, those with long 
narrow wings being swifter than the short-winged species; 
the stronger flying forms are apt to appear earlier in the 
evening than the others. 
Bats are endowed with a strong tactile sense, or something 
more than that, as they can note and avoid obstacles without 
contact; this sense seems to be in the wing-membranes, and 
possibly in the large ears and nose leaf, a curious complicated 
organ highly developed in some families^ Spazzani proved 
the existence of this sense by blinding bats, and letting them 
fly about a room across which many silk threads had been 
tied; they successfully avoided all contact with these threads 
though only space enough had been left between for them 
to pass with outstretched wings. 
The breeding season of bats is in the summer, and but one 
or two young are brought forth, as a rule. The young spends 
its infancy clinging to the under side of its mother. 
Key of the Colorado Families and Genera of Bats 
A. Tail not projecting beyond interfemoral membrane, but 
entirely enclosed within it {VespertilionidcB). 
a. Lower incisors, 6. 
a'. Ears separate and smaller, moderate in size, 
sl". Upper incisors, 4; mammae, 2. 
2i"' . Upper premolars, 6. Species all small, total length 
varying from 3 to 4; forearm, 1,25 to 1.60; tail 
long; ears narrow, in one species quite long; form 
slender; color mostly some shade of brown. 
Myotis, p. 271 
h'" . Upper premolars, 4; size small, length 4 or less, 
a"". Lower premolars, 6. Size larger, length 4 or less; 
forearm, 1.6; color very dark with silvery-tipped 
hairs; back of interfemoral membrane furred on 
basal third. Lasionycteris, p. 276 
h"" . Lower premolars, 4. Size very small, length, 3 
or less; forearm, 1.2; color pale; back of inter- 
femoral membrane sprinkled with hair on basal 
third. Pipistrellus, p. 277 
