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DISTRIBUTION AND ORIGIN OF SPECIES. 



The geographical distribution of animals over the terrestrial por- 

 tion of the globe, including its lakes, rivers, and stagnant pools, is 

 pretty well known as regards mammals, birds, reptiles, and fishes, 

 but of mollusks the record is as yet imperfect. Mr. Woodward 

 has given in his ' Manual ' a sketch of the general distribution of 

 molluscan life over the globe in geographical provinces and re- 

 gions, illustrated by lists of genera ; and I had the pleasure of 

 communicating, in 1851, to the ' Annals and Magazine of Natural 

 History,' an outline of the division of the terrestrial portion in pro- 

 vinces, founded on a detailed comparison of species. Objections 

 were, I believe, raised to my sketch of a system of geographical 

 provinces, on the ground that it was based on the distribution of 

 a single genus. That genus, however, JBuUmus, numbering eight 

 hundred species, is almost world-wide in its geographical range ; 

 and I found on the completion of my monograph of the great 

 genus Helix, which is cosmopolitan, and numbers after very con- 

 siderable reduction fifteen hundred species, that the distribution 

 of the two genera coincide, with the exception that Helix has an 

 important additional province in North America. Inland mollusks 

 are distributed throughout the globe in geographical provinces, 

 over which the species appear to disperse through migration or 

 transport, from that point or centre of each province in which the 

 species are most numerous, and most highly developed. Islands 

 that have been upheaved from beneath the bed of the ocean have 

 a molluscan fauna of their own. Madeira and the Galapagos 

 Islands, for example, possess an aboriginal offspring, small and of 

 insular character, quite distinct from the few species that have 

 become colonized in them by transmission from other lands. 



