518 LAND ANIMALS 



Islands there are 16 out of 35; and 5 out of 9 on Kerguelen. This is 

 further illustrated by the distribution of the weevil, Proterhinus, which 

 was described from Hawaii where 150 endemic species exist. One species 

 is known from Samoa, one from the Phoenix Islands, and two in the 

 Marquesas, one of the most isolated archipelagoes in the world. The 

 most closely related genus, Aglycyderes, is in the Canary Islands and 

 in New Zealand. These two genera now form a single family. There is 

 no apparent explanation for the occurrence of this related genus in 

 the Canary Islands. The New Zealand and other records are reason- 

 able with the Hawaiian Islands as a center of distribution. 4 



Amphibians and land mammals are unable to cross oceans, except 

 as they are accidentally transported, or introduced by man. The ab- 

 sence of mammals is especially notable in small islands, but even 

 New Zealand has so few small mammals, other than bats, that they 

 may be suspected of having been brought by Maoris. The absence of 

 amphibians and mammals is readily explainable, but why snakes, which 

 should be equally as agile as lizards, are so generally absent, is less 

 obvious. 



The stenohaline fresh-water animals have especial difficulty in 

 reaching islands, and they may be poorly represented even on un- 

 doubtedly continental islands, since they are exposed to extinction and 

 cannot be readily replaced. Poverty in fresh-water snails and complete 

 absence of fresh-water bivalves are characteristic of islands. The larger 

 East Indian islands, to be sure, have fresh-water snails, Anipullaria 

 and Pallidum, for example, in Celebes. Physa is known from Timor 

 and from the Fiji and Tonga islands, but is absent in the Moluccas 

 and in Polynesia. Neritidae, immigrants from the sea, replace them. 5 

 Aquatic insects are also entirely absent on most small islands. A single 

 water beetle is recorded from the Azores. The Hawaiian islands have 

 few aquatic insects, no caddis flies, for example, only 4 species of water 

 beetles and 2 aquatic Hemiptera. Dragonflies are widespread in islands 

 on account of their great powers of flight. 



Many islands, similarly, have few fresh-water fishes, or these may 

 be entirely absent. Large islands, close to the continents, with large 

 and permanent river systems, such as Borneo, may be rich in fishes. 

 Celebes, however, has only 3 species, and the poverty of the Pacific 

 islands in this respect is notable. Even the large island of Madagascar 

 has an impoverished fauna of true fresh-water fishes: 2 silurids, 2 

 cyprinodonts, 1 atherinid, 4 cichlids, and 7 gobies, the last undoubtedly 

 recent immigrants from the sea. 6 



A considerable number of marine fishes enter fresh water, and such 



