248 SATS. 



cannot be extended in an upward direction beyond the limits of the impetus of the 

 original leap. 



This power of true flight is, then, the essential characteristic of all bats ; and 

 it is a very remarkable fact that among all the host of extinct animals with which 

 we are now acquainted, none have been discovered in any way connecting bats with 

 other Mammals. Indeed, remains of bats very closely resembling existing kinds 

 are met with in the upper part of the Eocene period, which show that the order 

 is a very ancient one, and that we should have to go back still earlier before 

 creatures intermediate between bats and other Mammals were met with. In spite 

 of this, naturalists have, however, no hesitation in believing that bats have taken 

 origin from Mammals of ordinary terrestrial habits. It is found, indeed, that in 

 their essential structure bats are so closely allied to the Insectivores (of which 

 we treat next), such as shrews, moles, etc., that there can be little doubt of their 

 derivation from the ancestral forms of that order; and it is probable that the 

 power of true flight was developed gradually from spurious flight, like that of 

 flying squirrels. Moreover, it will be shown later on that there is a very curious 

 kind of Insectivore, endued with the power of spurious flight, which may give us 

 some inkling of the manner in which bats have been derived from the earlier 

 members of that order of Mammals. Bats are accordingly regarded by zoologists 

 as neither more nor less than Insectivores, specially modified and adapted for an 

 aerial life. Moreover, as there appear to be indications that the Insectivores were 

 connected with some of the extinct lemurs, it is now considered best to place them 

 and the bats immediately after the Primates. This must not, however, be taken 

 as any indication that these groups really occupy a high position in the zoological 

 scale ; the fact really being that their organisation is of a low type, and far 

 inferior to that of the Carnivores which are placed later on. 



The most obvious and important characteristic of bats being 



Characteristics. _ r . . . . , 



their faculty or flight, and the apparatus for this being mainly 



furnished by the fore-limb, the order to which they belong has been appropriately 

 named Chiroptera, or hand- winged. In the great majority of Mammals the hind- 

 limbs are as large as, or larger than, the front pair, but in bats the latter (as is. 

 well shown in the figure of the skeleton at the head of this chapter) vastly 

 exceed the former in length. In a bat's wing the humerus of the upper 

 arm is only moderately elongated, but the single complete bone in the fore- 

 arm, corresponding to the human radius, has a far greater length, and this ex- 

 traordinary elongation is carried to a still greater extent in the bones of the 

 hand, all of which, with the exception of those of the thumb, form long slender 

 rods. The thumb is free, and terminates in a hooked claw, which can be used for 

 the purposes of climbing or suspension ; but the fingers, of which the third is the 

 longest, are connected together by the delicate membrane constituting the soft part 

 of the wing. This wing-membrane is continued along the arm and the sides of the 

 body, and thence to the hind-legs. There is, moreover, a similar membrane 

 connecting the two hind-limbs with the generally long tail ; this membrane being 

 usually supported by a peculiar spur of bone projecting from the foot. The toes 

 are, however, quite free. In consequence of the connection of the hind-limb with 

 the wing-membrane, the knee-joint is directed backwards instead of forwards in 



