BARRIERS AND MEANS OF DISPERSAL 67 



insects apparently carried up by the winds since they neither develop 

 there nor feed in that zone as adults. They are especially subject to 

 being blown away from such exposed situations. 49 



Bats, in consequence of their powers of flight, also exhibit wide 

 distributions of their species and genera. Many species inhabit almost 

 the entire Old World, such as Miniopterus schreibersi and Vesperugo 

 noctula; V. serotinus extends into the tropics in Africa (Gaboon) and 

 Asia, and colonizes the corresponding latitudes in America from the 

 Antilles to Lake Winnipeg. Broad stretches of ocean do not seem to 

 be crossed by bats of their own accord, and most species of fruit-eating 

 flying foxes of Malaysia and Polynesia are restricted to particular 

 groups of islands. 50 The occasionally fish-eating Noctilio leporinus 

 appears on all the West Indian islands, without the formation of local 

 races ; other species of bats have frequently developed special subspecies 

 on the various islands of the Antilles. 51 



Though flight reaches its highest development among birds, there 

 are great differences in the flying power of various groups. Some birds 

 of prey such as the sea eagle and the barn owl have an almost world- 

 wide distribution; the stork journeys from east Prussia to Cape Colony 

 and back every year, and the golden plover does the same from 

 Venezuela to Labrador; in contrast with these, many other birds are 

 restricted to relatively small areas. The gallinaceous birds, such as 

 the pheasants, which are poor fliers, have relatively restricted ranges. 

 The members of the heavy-flighted auks are so different on the two 

 coasts of North America that, of 17 Pacific and 9 Atlantic species, 

 only one {Cepphus mandtii) is in common. 52 Finally, for some species, 

 such as petrels and gulls, the ocean not only is not a barrier, but 

 actually becomes a source of food and a place of rest. Powerful fliers 

 of these groups belong to the most widely distributed birds. 



Passive distribution of terrestrial animals takes place in various 

 ways. Storms carry dust and twigs and leaves many miles, and thus 

 transport not only resting stages of Protozoa and small Metazoa, but 

 also small snails, myriapods, insects and spiders, and their eggs. The 

 "Pampero," a southwest wind from the Pampas, brings a veritable 

 rain of insects to Buenos Aires and Montevideo. Many insects are 

 blown up to the glaciers in our high mountains; large larvae of a goat 

 chafer {Aegosoma scabricorne) fell to the ground during a thunder- 

 storm in Basel. 53 Rains of caterpillars which were brought by storms 

 are reported in south Russia, and of springtails (Collembola) in 

 Balwyn, Victoria. Spiders with their flight threads have blown onto 

 the rigging of ships 300 km. from land. Only free-living spiders are 

 transported by this means, and these accordingly are the only kinds of 



