OF ISLAND FAUNAS 155 



time mammals were evolving rapidly and spreading 

 widely. 



2. "When an island has been separated from adjacent 

 land masses for a moderately long time, i. e. since the 

 middle of the Tertiary period, it will tend to have 

 a rich fauna, including representatives of all the chief 

 classes and phyla, but the more modem classes will be 

 represented by primitive forms, their primitiveness 

 depending on the length of the period during which the 

 island has been isolated. Of such islands Madagascar 

 and the adjacent islands of the Indian Ocean are good 

 examples. 



3. When the separation of an island from the adjacent 

 continent has taken place within geologically recent 

 times, i. e. in the Pleistocene or Post-Pleistocene period, 

 the faima wiU be in all essentials similar to that 

 of the adjacent land mass, though minor differences 

 may occur. Examples are the British Isles, Japan, 

 Borneo, Java, &c. 



In other words, the most satisfactory classification 

 of islands from the point of view of their fauna depends 

 upon the approximate length of time since which they 

 have been isolated. 



Reeebences. Wallace's Island lAfe (second edition, London, 1892) is 

 the classical work dealing with the subject, which is also discussed to 

 a minor extent in the same author's Darwinism. A very interesting 

 account of the Galapagos Islands will be found in Darwin's Journal of 

 Researches into the Natural History and Oeology of the Countries visited 

 during the Voyage of the ' Beagle ' (London, 1843). The subject is also 

 fully treated in Bcddard's Text-book of Zoogeography (Cambridge, 1895). 

 See also Dobson's, On Some Peculiarities in the Oeographical Distribution 

 and in the Habits of certain Mammals inhabiting Continental and Oceanic 

 Islands {Ann. Nat. Hist. xiv. 1884). 



