INTRODUCTION. v 



delightful " Malay Archipelago," first published in 1869, cannot 

 know all the treasures given to science by Mr. Wallace's eight 

 years' expatriation, for before writing his travels he had con- 

 tributed no fewer than eighteen papers to the transactions or 

 journals of the Linnean, Zoological, and Entomological Societies, 

 and twelve articles to various scientific periodicals, while in his 

 subsequent volumes on "Natural Selection," 1 871, his monumen- 

 tal work on the "Geographical Distribution of Animals," 1876, 

 on "Tropical Nature," 1878, and on "Island Life," 1880, he laid 

 open still more fully his accumulations of travel and thought in 

 both hemispheres. One of the most valuable results of his travels 

 in Malaysia was the establishment of a line dividing the archi- 

 pelago into two main groups, Indo-Malaysia and Austro- 

 Malaysia, marked by peculiar species and groups of animals. 

 This line, now everywhere known as Wallace's line, is marked 

 by a deep sea belt between Celebes and Borneo, and Lombok 

 and Bali respectively ; and it is curious that a similar line, but 

 somewhat further east, divides on the whole the Malay from 

 the Papuan races of man. The new facts on butterflies, on 

 birds of paradise, on mimicry between various animals and 

 plants, and on the Malay and Papuan races are only a few of 

 the subjects of intense interest illuminated by Mr. Wallace as 

 the result of his travels in Malaysia. 



In a paper in the Annals and Magazine of Natural History 

 for September, 1855, " On the Law that has regulated the Intro- 

 duction of New Species," Mr. Wallace had already drawn the 

 conclusion that every species has come into existence coinci- 

 dent both in space and time with a pre-existing closely allied 

 species. In the same paper is a brief expression of the 

 idea which Mr. Darwin expanded into one of his fine 

 passages comparing all members of the same class of beings 

 to a great tree. The varied facts of the distribution of animal 

 and plant life, set forth and explained in this paper, foreshadow 

 the author's future great work on the subject. Mr. Darwin, 

 already an observer and student of long standing on the 

 question of the origin of species, had noted this paper and 

 agreed to the truth of almost every word of it. In October 

 1856, Mr. Wallace wrote to Mr. Darwin from Celebes, and 

 in replying to his letter Mr. Darwin, on May 1st, 1857, said 

 he could plainly see that they had thought much alike, and 

 had to a certain extent come to similar conclusions ; and later 



