GEOGRAPHICAL DISTRIBUTION AND DESCENT. 



in 



man from one island group in the Pacific 

 Ocean to another; but their powers of flight 

 are so great that they were no doubt able to 

 cross the intervening seas without other 

 assistance. 



Both smooth-nosed and leaf-nosed bats are 

 spread over the whole world wherever there 

 are insects enough for their food; and only in 

 the case of the latter group can any sort of local 

 limitation be noted. Among these the true 

 horse-shoe bats are altogether excluded from 

 America, the vampires, on the other hand, 

 almost entirely confined to South America, 

 only one species pressing as far north as 

 Southern California. Tropical South America 

 is thereby, as well as by the absence of flying 

 foxes, shown to be an originally isolated 

 region. 



Concerning the derivation of the bats as 

 such from older types, palaeontology affords 

 us no information whatever. The remains 

 found in the more recent, and especially in 

 Quaternary deposits, belong, except for slight 

 variations, to genera and species still living, 

 and the oldest bat yet discovered, that found 

 in the Eocene gypsum of Montmartre, and 

 accordingly in an early deposit for placental 



mammals, is closely allied to the genus 

 Vespertilio. The great variety of the genera 

 now living, and the wide distribution of in- 

 dividual types, are just as strong evidence 

 of the great age of the bats as the structure 

 of their dentition, which connects them im- 

 mediately with the insect-eating marsupials, 

 and even as the form of the wings themselves, 

 which, as has already been shown in detail, 

 are merely a special development of an 

 embryonic, and consequently very primitive 

 character. Looking at these relations we 

 could not be very much surprised if it should 

 turn out some day that transitional forms 

 were found connecting the flying-bats with 

 swimming ancestors, without there being any 

 line of development through four-footed land 

 animals. These, however, are only con- 

 jectures, for so far the structure of the bat's 

 wing stands by itself without any analogue to 

 place beside it. Only that of the flying 

 reptiles, the pterodactyls, presents some in- 

 teresting points of comparison, while the 

 bird's wing, in which we can see the result 

 of a gradual transformation of a reptilian 

 foot, has arisen out of totally different con- 

 ditions. 



