HISTORICAL ZOOGEOGRAPHY 



115 



stocks of the marine Cerithium which have entered brackish water in 

 different parts of the world (cf. p. 197). 



The ancient crustaceans of the family Anaspididae, restricted to 

 the fresh waters of Australia and Tasmania and to underground springs 

 in Europe (Bathynella) , 52 have a strikingly discontinuous distribution. 

 Their Paleozoic relatives Uronectes and Palcocaris, indicate a formerly 

 much wider distribution. 



It is by no means a mere assumption that the northern forms are 

 more advanced. Their superiority has been shown by the practical 

 experiment of introduction. Eurasian forms introduced into Australia 

 and New Zealand have frequently been able to displace the native 

 forms of similar habits. Thus the two predatory marsupials, the 



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20 



20 



40 



60 



__._V^- 



XL. 



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Fig. 9. — Distribution of Galaxias. After Boulenger. 



Tasmanian wolf, Thylacinus, and the Tasmanian devil, Sarcophilus, 

 have survived only in Tasmania, and doubtless became extinct in 

 Australia on account of the competition of the placental dingo {Canis 

 dingo), an immigrant or introduction from the north, which has not 

 reached Tasmania. 



The native Australian songbirds are being crowded out by the 

 forms introduced from Europe, such as the sparrow, starling, black- 

 bird, goldfinch, and greenfinch. 53 The skylark is rated the second 

 worst bird pest in New Zealand. The goldfish (Carassius auratus) , 

 which was introduced in Madagascar, is crowding out the native fishes 

 wherever it comes into competition with them. 54 European ants and 

 earthworms have spread in South Africa, South America, Australia, 

 and New Zealand, at the expense of the native species. In the reverse 

 direction, of 490 exotic species of animals known to have been brought 

 into Hamburg by shipping in the course of three years, only 5% could 

 maintain themselves, and these only in greenhouses, in tanbark, and 



