524 
MAMMALIA. 
developed, tlie senses of tlie Bats are of an astonishing extent and 
subtlety. 
In general the ears are large, widely open, and the perception 
of sounds perfect. With regard to smell, it is extremely delicate. 
In a number of species tbe entrance to the nostrils is covered by 
membranous folds called nasal-leaves, which endow the olfactory 
organ with a singular power. Lastly, the sense of touch is 
exquisite ; a circumstance that cannot surprise us when we con- 
sider the wide extent of their hands. 
It is to this exceptional delicacy of touch that must be attri- 
buted the ease with which Bats fly about in their dark retreats 
without striking against the angles, rocky projections, or other 
objects. Spallanzani instituted experiments which were decisive 
in this respect. The celebrated physiologist destroyed the vision 
of several specimens, and on leaving them alone he saw them fly 
around the room without betraying the slightest hesitation, or 
without striking their heads against the furniture or the ceiling ; 
in a word, without the deprivation of sight having changed in the 
slightest degree their conditions of existence. 
This fact induced Spallanzani to declare that Bats are endowed 
with a sixth sense, which informs them of the proximity of solid 
bodies. But such an explanation is unnecessary. When we are 
aware of the prodigious sensibility of the tactile organs in these 
animals, we may admit that they are affected by certain movements 
of the air which are imperceptible to us, and that Bats can thus 
be rendered conscious of the proximity of a body by the obstruction 
to the eddies and currents of air displaced by them in their flight. 
In cold and temperate regions Bats hybernate. They are then 
absolutely insensible, and may be handled, shaken, and even 
thrown in the air, without betraying the least movement. But 
if they are held for some time in the hands, or near a fire, under 
the influence of the heat they rapidly show signs of animation. 
During the period of torpidity the vital functions are executed 
feebly, but they are not altogether abolished. They cannot dis- 
pense with nourishment during this portion of their existence, 
but as they are incapable of taking food, they devour their own 
substance, the fat that has accumulated in their bodies during 
the period of activity. In this way is explained their emaciation 
at the termination of their winter sleep. 
