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 termi- 

 nates 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 recognized 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, distinguished from 

 one another by several easily recognized features. In the first section one of the 

 chief characteristics is that the tail is included within the membrane 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. 



(263) 



