THE DISTRIBUTION OF SPECIES. 20I 



man, open to their invasion. Facts of this sort are the 

 "enormous increase of rabbits and pigs in Australia 

 and New Zealand, of horses and cattle in South America, 

 and of the sparrow in North America, though in none 

 of these cases are the animals natives of the countries 

 in which they thrive so well." (Wallace.) The persist- 

 ent spreading of European weeds to the exclusion of 

 our native plants is a fact too well known to every 

 farmer in America. The constant movement westward 

 of the whiteweed and the Canada thistle marks the 

 steady deterioration of our grass fields. Especially 

 noteworthy has been this change in Aus- 

 Invasion of the ^^.^jj^ ^^^^ ^^^ Zealand. In New Zea- 

 land the weeds of Europe, toughened by 



realm. r 7 o 



centuries of struggle, have won an easy 

 victory over the native plants. Edward Wakefield, in 

 his history of New Zealand, says that "many animals 

 and birds acquire peculiarities in the new country which 

 would indeed astonish those accustomed to them in the 

 old. They usually run to a much larger size and breed 

 oftener. They also take to strange kinds of food. 

 Birds deemed granivorous at home become insectivorous 

 here, and vice versa. Some learn the habits of the na- 

 tive species. Skylarks imitate the native wagtail, and 

 may often be seen perching on fences and telegraph 

 wires. They sing in the nighttime, too, a thing un- 

 heard of in the old country, and doubtless acquired from 

 the nocturnal habits of the New Zealand birds." 



The European house fly in New Zealand has com- 

 pletely extirpated the large bluebottle fly, which was 

 formerly a source of great annoyance to the settlers. 

 An account is given of a farmer who filled a bottle with 

 house flies and carried them eighty miles into the coun- 

 try, liberating them, one by one, in the vicinity of his 

 sheepfolds, in order to let them take the place of the 



