154 SPECIAL FEATURES 
degree of specialization along their own lines, and have 
evolved in many different directions. 
If we sum up the more important general points in 
regard to island faunas, we may note first that Wallace’s 
distinction into oceanic and continental islands is not 
of very great practical importance, because the pro- 
gress of geology, since the classification was laid down, 
has made it difficult to apply. It involves a conception 
of the permanence of ocean basins which is not now 
generally accepted. Thus, while Wallace names the 
Galapagos group as a characteristic oceanic group, 
others believe that the presence of giant land tortoises 
is in itself a proof of a former land connexion. For 
our purpose then it is sufficient to recognize the follow- 
ing three conditions : 
1. When an island has never had a connexion with 
a continent, e.g. many coral and volcanic islands, or 
has only had such a connexion at a geologically remote 
period (Galapagos?) before the higher forms living at 
the present day had originated, or before they had had 
time to become widely distributed, its fauna contains no 
mammals, no amphibia, (1) no reptiles, or (2) reptiles of 
a very primitive type, or (3) such as could be accident- 
ally carried by floating wood, &c. The most important 
members of its fauna will be birds, insects, and land 
shells. Owing to the isolation the animals will tend to 
exhibit special peculiarities, fitting them for their 
habitat. Among flying forms the conditions favour 
those in which the power of flight is moderately de- 
veloped, or has disappeared. Examples of such islands 
are the Azores, the Bermudas, St. Helena, the Sand- 
wich Islands, &c. Where such islands have had a 
continental connexion, this must have been prior to 
the deposition of the lower Tertiary beds, for at this 
