320 Geographical Distribution of Aimnals 



this anatomist dealt with some of the fundamental causes of distri- 

 bution. 



^Vllilst Tiedemann restricted himself to Birds, A. Desmoulins in 

 1822 wrote a short but most suggestive paper on the Vertebrata, 

 omitting the birds ; he combated the view recently proposed by the 

 entomologist Latreille that temperature was the main factor in distri- 

 bution. Some of his ten main conclusions show a peculiar mixture 

 of evolutionary ideas coupled with the conception of the stability of 

 species : whilst each species must have started from but one creative 

 centre, there may be several " analogous centres of creation " so far 

 as genera and families are concerned. Countries with different 

 faunas, but lying within the same climatic zones, are proof of the 

 effective and permanent existence of barriers preventing an exchange 

 between the original creative centres. ' 



The first book dealing with the " geography and classification " of 

 the whole animal kingdom was written by W. Swainson^ in 1835. He 

 saw in the five races of Man the clue to the mapping of the world 

 into as many "true zoological divisions," and he reconciled the five 

 continents with his mystical quinary circles. 



Lyell's Principles of Geology should have marked a new epoch, 

 since in his Elements he treats of the past history of the globe and 

 the distribution of animals in time, and in his Princ'qjles of their 

 distribution in space in connection with the actual changes undergone 

 by the surface of the world. But as the sub-title of his great work 

 ''Modern changes of the Earth and its inhabitants" indicates, he 

 restricted himself to comparatively minor changes, and, emphatically 

 believing in the permanency of the great oceans, his numerous and 

 careful interpretations of the effect of the geological changes upon 

 the dispersal of animals did after aU advance the problem but 

 little. 



Hitherto the marine faunas had been neglected. This was 

 remedied by E. Forbes, who established nine homozoic zones, based 

 mainly on the study of the mollusca, the determining factors being 

 to a great extent the isotherms of the sea, whilst the 25 provinces 

 were given by the configuration of the land. He was followed by 

 J. D. Dana, who, taking principally the Crustacea as a basis, and 

 as leading factors the mean temperatures of the coldest and of the 

 warmest months, established five latitudinal zones. By using these 

 as divisors into an American, Afro-European, Oriental, Arctic and 

 Antarctic realm, most of which were limited by an eastern and 

 western land-boundary, he arrived at about threescore provinces. 



^ "A Treatise on the Geography and Classificatiou of Animals," Laalner's Cabinet 

 Cyclopaedia, London, 1835, 



