CHAPTER X. 
Bats,— continued . 
The Insect-Eating Bats {Microchiroptera). 
Having treated in the preceding chapter of the bats which feed entirely upon 
fruit or flowers, we now come to the consideration of the much larger group of 
those which subsist upon insects, among which we must include a few which have 
acquired frugivorous habits, and likewise those which subsist by sucking the blood 
of Mammals larger than themselves. As being generally of much smaller size than 
those of the frugivorous group (Megachiroptera), the members of the insectivorous 
group of bats are collectively known to zoologists as the Microchiroptera; and it 
remains to indicate the leading characteristics (apart from those of an anatomical 
nature) by which this group may be distinguished from the one treated in the 
preceding chapter. 
Apart from their generally inferior bodily size, the insectivorous bats are 
broadly distinguished from the fruit-bats by the presence of a number of sharp 
cusps on the crowns of their molar teeth; these cusps in the upper molars taking 
the form of the letter W. There is, moreover, no trace of the longitudinal groove 
found in the molars of the fruit-bats; the upper molars having their longer 
diameter placed transversely, instead of longitudinally. Another distinctive 
feature is to be found in the index finger of the fore-limb, which has never 
more than two joints, and usually contains but one; moreover, this finger never 
terminates in a claw, as it so frequently does among the fruit-bats. Then, 
again, the head of an insect-eating bat may be at once recognised by the two 
margins of the conch of the ear arising from the head from separate points, instead 
of forming a complete ring at the base, as in the fruit-bats. Moreover, the tail, 
which is very generally present and of considerable length, is either contained in 
the membrane joining the hind-limbs, or is visible upon the upper surface of the 
same. The insect-eating bats are further divisible into two minor sections, dis¬ 
tinguished from one another by several easily recognised features. In the first 
section one of the chief characteristics is that the tail is included within the mem¬ 
brane between the hind legs. Another is that the inner pair of incisor teeth in the 
upper jaw are never very large, and are always separated from one another in the 
middle line by a considerable space. Yet another characteristic of these bats, with 
the exception of three species (belonging to as many genera), is that the third, or 
middle, finger has only two bony joints; to which it may be added that when the 
animals are at rest it will be found that the first joint of the same finger is 
invariably extended in the same line as its supporting metacarpal bone. 
