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. 



