DERIVATION OF THE FLORA AND FAUNA 349 



The Homoptera present the same picture in Hawaii, about 350 native spe- 

 cies, most of them endemic and suggesting a southwest Pacific ancestry. Of the 

 species reported from Juan Fernandez only one-third have been described, all 

 endemic and as far as we know with their relatives in the south and central Pacific. 



No order characteristic of insular faunas has aroused greater interest among 

 biogeographers than the Pacific larid molluscs, nowhere more wonderfully devel- 

 oped than in the Hawaiian chain. In the discussion of land connections they 

 occupy a central position. 



Wallace found that the wide distribution of the land snails is "by no 

 means so easy to explain as that of the insects"; the chances have been "rare 

 and exceptional", possibly eggs stuck to the feet of aquatic birds, or the animals 

 themselves were storm-carried, "attached to leaves and twigs" — this would be 

 the only means by which viviparous forms could be transported. 



GULICK [iig] treats the land-shell problem at some length. Speaking of Easter 

 Island he asserts that "hurricanes spread gravid land-snails as dust over almost 

 as great distance as plant seeds can be blown", but he gives no facts to support 

 this very positive statement. The land-shells of Juan Fernandez and Saint Helena 

 are then remarked upon. 



At least three elements can have derived their ancestry only from Polynesia, fully 

 3400 miles away, unless Easter Island served as a way station. 



The archaic complexion of the snail fauna is not necessarily very significant, as 

 younger continental forms do not for the most part yield minute, easily wind-blown 

 species. 



Archaic — exactly, malacologists emphasize that more modern types do not occur 

 on oceanic islands unless brought by man, and this has, naturally enough, been 

 used as an argument in favour of early land connections before the modern types 

 existed. In Gulick's view the size, not the age, decides. 



Large, softskinned creatures invariably make a poor showing . . . large helices ex- 

 amplify this disability so excellently that their failure to arrive is a sort of negative 

 criterium for insularity (p. 414). 



But neither are all continental species large, nor all insular ones small, and the 

 oceanic snail fauna includes many forms that cannot spread like dust. GULiCK 

 remarks on the genus Partula that "its 120 geographically restricted species mostly 

 weigh too much and are too tender to fit easily into theories of transport by 

 air or sea", and this makes him take into account the possibilities of "land ridges" 

 to facilitate transport. 



"It is evident", he says p. 419, "that the vast diversification is a proof of 

 the great local antiquity of these families, and hence of a considerable antiquity 

 of their island habitat." This is not true of the islands as they appear now^ and 

 as they have stood for probably millions of years. 



Land snails, just as weevils, are dispersed by some unknown method, UsiN- 

 GER thinks (I.e. 315), while Mayr, as already quoted, regarded the presence of 

 small molluscs on oceanic islands as a proof of the efficiency of hurricanes, but 

 later on expressed himself as follows. 



