WHAT ARE BATS? 
229 
bird, both the muscles which strike the wings downwards, and 
those which raise them upwards, are both together placed upon 
the breast, and hence its much deeper and more conspicuous keel. 
Still, though the muscular structure of the breast of a bat 
is not so perfectly arranged for flight as is that of a bird, it is 
an approximation to bird structure, and one we can well under- 
stand from the similarity of action. But it may puzzle some of 
my hearers at first to think why the mole, of all creatures in the 
world, should have a breast-bone at all like that of a bird. But 
a moment’s reflection will make it obvious that the mole also 
requires most powerful breast muscles, in order that it may dig 
its way through the soil with the wonderful speed with which 
it does dig through it. Similar causes produce similar effects, 
and thus it is that the mole, like the bat and the bird, comes to 
have a keeled breast-bone. 
The membrane of the bat’s wing is a structure of extreme 
and peculiar delicacy as regards the sense of touch, and the 
perfection of this sense is doubtless contributed to by a special 
condition of its blood-vessels. Although the sense of touch de- 
pends, of course, directly on the nerves, the functional activity of 
the nerves depends upon the quantity and the sufficiently rapid 
renewal of the blood sent to them. This is shown by the 
familiar examples of numbness brought about by checking the 
supply of blood to any part with a ligature, as also by the 
increased sensibility occasioned by inflammation ; that is, through 
a more copious supply of blood. Now, in most animals, as in 
ourselves, the heart pulsates with rhythmical contractility : but 
the blood-vessels which distribute the blood over the body are 
not themselves contractile, however highly elastic they may be. 
In the bat’s wing, however, the vessels which convey blood towards 
the heart (i.e. the veins) have been found by Dr. Wharton Jones 
to be themselves positively contractile, and so fitted in a most 
exceptional manner to help on the blood supply, thus indirectly 
augmenting the power of touch. 
This exceptional condition of the vascular system may then 
have something to do with that exceptional perfection of the 
power of sensation before referred to, and which was experiment- 
ally demonstrated by Spallanzani. He found, not having the fear 
of anti-vivisectionists before his eyes, that bats deprived of 
sight, and as far as possible also of smell and hearing, were still 
able not only to avoid ordinary obstacles to their flight in 
strange localities, but even to pass between threads purposely 
extended in various directions across the room in which the 
experiments were made. This skill it is believed is due to an 
excessively delicate power of sensation possessed by the flying 
membrane — a power enabling the creatures by atmospheric 
pressure and vibration to feel, before contact, the nearness of 
