inhabiting Continental and Oceanic Islands. 155 



"bution of the flying-foxes, for not a single species of Pteropus 

 is known from Africa, though they abound in Madagascar 

 and the Comoro Islands. On the other hand, the insectivorous 

 bats, with much greater powers of flight, are very similar in 

 Madagascar and Africa. 



But it may be urged that such propinquity of islands to 

 one another and to these continents would also permit inter- 

 change of the avifaunas. 



To this the following reply may be made : — That the 

 existence of a complete chain of islands separated by suffi- 

 ciently narrow straits may have existed for a short period 

 only, the completeness of the chain being, perhaps, dependent 

 on some volcanic group, which may have disappeared as sud- 

 denly as it came into existence. Under such circumstances 

 bats would be much more likely to establish themselves 

 successfully in the new continental lands open to their migra- 

 tions for the following reasons: — (1) that the food of both the 

 frugivorous and insectivorous species is of a more general 

 character than that of birds, few of the species of which are 

 so omnivorous, within these limits, as the bats ; (2) that the 

 nocturnal habits of the bats would enable them to escape ob- 

 servation from enemies always sure to recognize the presence 

 of solitary individuals. 



It may now be urged that if we acknowledge the effect of 

 such circumstances in favouring the distribution of bats, we 

 ought then to expect to find more bats than birds in all 

 oceanic islands. Buch an objection may be easily disposed 

 of when it is remembered that volant insects are very scarce 

 in all oceanic islands, whereas they are abundant in all con- 

 tinents, and, furthermore, that a straggling bird on arrival at 

 an oceanic island would encounter far fewer enemies than it 

 would meet in a continent, and, owing to its power of seeking 

 its food on foot as well as on wing, would also be much more 

 likely to survive than the thoroughly aerial bat. 



It is, I believe, to a great extent, on this very principle, that 

 the Chiropterous fauna of New Zealand is so limited ; that, 

 as yet, two species of bats only, represented apparently by 

 few individuals, are known from these islands, while in the 

 British Isles, which about equal them in extent, there are 

 eight times the number of species, and, probably, a far greater 

 proportion of individuals. The striking paucity of winged 

 insects which, in other countries of corresponding climate, 

 form wholly the food of the bats, has evidently, in a great 

 measure, not only caused this remarkable difference, but, as I 

 pointed out some years ago for the first time, has led to a 

 change in the structure of one of the two species comparable 



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