THE ZOOLOGIST 



FOR 1852. 



Notes on the Zoology of the Isthmus of Panama. 

 By Berthold Seemann, Esq., late Naturalist to H. M. S. Herald. * 



America is generally divided into two zoological provinces, sepa- 

 rated from each other by the barrier presented by the Mexican table- 

 land. That the divisions are well characterized, few are inclined to 

 dispute ; but, it may be asked, was or is the barrier sufficient to check 

 the progress of species ? Confining ourselves to the tropics, it is 

 possible to migrate from Guayaquil to Mazatlan, which may be consi- 

 dered their extremes on the western coast, without changing the tem- 

 perature more than a few degrees — without ascending any mountains 

 possessing a physical constitution different from that of the lower 

 equinoctial region. That this passage has been adopted, is evident 

 from the presence of several South-American species in Northern 

 America. That many animals have passed the Isthmus without stop- 

 ping is also proved. The armadillo, for instance, which indisputably 

 belongs to South America, is found in no part of Panama, but again 

 appears in the neighbourhood of Mazatlan, in latitude 23° 12' N. 

 It is no less evident that the migration of animals, if not otherwise 

 restricted by the change of food &c, could avoid the Mexican table- 

 land by pushing from the North along the Gulf of California, a route 

 which, according to recent researches, was that taken by the Aztec 

 nations in passing to the plains of Anahuac. The Isthmus, therefore, 

 in connecting the American continent, furthers not only the distribu- 

 tion of plants, but also offered facilities for the migration of animals, 

 and without this passage many genera and species, now common to 

 both countries, would probably have been confined to one. 



* The following Notes will appear in M. Seemann's forthcoming work, — 'The 

 Isthmus of Panama : Historical and Descriptive.' 



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