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 modern 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 fauna will 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. 
REFERENCES. Wallace’s Island Life (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 Geology of the Countries visited 
during the Voyage of the ‘ Beagle’ (London, 1843). The subject is also 
fully treated in Beddard’s Tezxt-book of Zoogeography (Cambridge, 1895). 
See also Dobson’s, On Some Peculiarities in the Geographical Distribution 
and in the Habits of certain Mammals inhabiting Continental and Oceanic 
Islands (Ann. Nat. Hist. xiv. 1884). 
