GEOGRAPHICAL DISTRIBUTION. 75 



A species spread thnnigh two zones of temperature also varies ; 

 many European species, according to McLachlan, becoming 

 "melanized" in going northward, while others become paler. 

 ISuch varieties have been described as difterent species. 



Mr. Alfred Wallace finds that the most constant forms of 

 species are those the most limited in their geographical range 

 as to a particular island, while those species, which range over 

 a large part of the Malayan Archipelago, vary very consider- 

 ably. It is a general rule throughout the animal and vegetable 

 world, that the most widely spread species are those capable of 

 withstanding the greatest climatic changes, and adapting them- 

 selves to the greatest diversities of topography. 



While the most widely distributed species are thought to be 

 the most variable, Mr. Scudder finds in the genus Chionchas 

 that C. semidea, restricted to the summit of Mt. Wasliington 

 varies almost as much as C. Oeno, which is circumpolar, being 

 found both in Labrador and Northern Europe. 



Mr. Wallace (Transactions of the Linnjean Society, xxv, 

 1865, p. 14) mentions the following facts "as showing the 

 special influence of locality in giving a peculiar fades to the 

 several disconnected species that inhabit it." 



"On examining the closely allied species, local forms, and 

 varieties distributed over the Indian and Malayan regions, I 

 find that larger or smaller districts, or even single islands, give 

 a special character to the majority of tlieir Papilionidii?. For 

 instance: 1. The species of the Indian region (vSumatra, Java, 

 and Borneo) are almost invariably smaller than the allied spe- 

 cies inhabiting the Celebes and Moluccas ; 2. The species of 

 New Guinea and Australia are also, though in a less degree, 

 smaller than the nearest species or A'arieties of the Moluccas ; 

 o. In the Moluccas themselves the species of Amboyna are larg- 

 est ; 4. The species of Celebes equal or even surpass in size those 

 of Amboyna; 5. The species and varieties of Celebes possess 

 a striking character in the form of the anterior Avings, differing 

 from that of the allied species and varieties of all the surrounding 

 islands ; 6. Tailed species in India or the Indian region become 

 tailless as they spread eastward through the archipelago." 



Variety breeding. Varieties may be produced artificially ; 

 thus negro varieties of insects ma}- be raised "from parents 



