DERIVATION OF THE FLORA AND FAUNA 345 



This is quite true, but will not the result become much the same with land 

 connections? The main source of the fauna is the same, the similarity is a con- 

 sequence, and local endemism is a result of isolation. 



Acarids present the same problem. MUMFORD [183) remarks that is is very 

 difficult to compile lists of species for the Pacific islands and that, at present, 

 no safe conclusion can be drawn with regard to the distribution of genera. This 

 is true, but we know that numerous indigenous species occur and that local en- 

 demism seems to be high. How these extremely delicate little animals would be 

 able to stand long overseas voyages is difficult to imagine. They are plentiful in 

 humid forest soils on Juan Fernandez and all the species except two adventitious 

 ones are endemic. Little is known of their relationships. If washed down from 

 the hill-sides and carried out into the sea, they will die — only wind transport 

 remains. Pseudoscorpio7is may be more resistant to both salt water and desicca- 

 tion, but their pronounced endemism bears witness of long isolation. All the false 

 scorpions recorded from Juan Fernandez are endemic, and there is one endemic 

 genus. They were unknown when MuMFORD (I.e. 246) wrote: 



As Chamberlain points out, it is doubtful whether anything like true insular endemism 

 occurs in most species of false scorpions because of the ease with which they are distrib- 

 uted. 



They are well adapted to be carried about by man. Among the Myria- 

 poda are many local endemic species. These creatures are, according to my own 

 experience, rather tough and might be able to spread by the same methods as 

 earth-worms and land crustaceans. It is not very probable that they are blown 

 from continents to distant islands. Cosmopolitan forms are probably adventitious. 

 If this applies also to Collembola I do not know; very wide-spread species may 

 be so ancient that they have attained their distribution when the map of the globe 

 was quite different from the present one. It is unlikely that they are able to 

 migrate overseas. Lindsay [i6y. 7 1 9) writes : 



The primitively wingless Collembola seem to constitute better material for distribution 

 studies than any other insect order, because migration by flight is imp'ossible and the 

 delicate integument makes it very unlikely that the insect could be carried any appre- 

 ciable distance by the sea. 



We can safely add that, if blown out over the ocean, they would soon perish. 

 Zimmerman suspects that none of the 32 species recorded for Hawaii is indige- 

 nous there; thus, all are supposed to have been imported by the traffic. How- 

 ever, 3 species are supposed to be endemic in Juan Fernandez. Two species of 

 the Hawaiian Thysanuva are "possibly endemic" (Zimmerman) but perhaps adven- 

 titious. These creatures do not appear to be fit for long-distance dispersal, and 

 the two species known from Juan Fernandez are endemic. One of them belongs 

 to a monotypical genus with Australian affinities, a disjunction not easily bridged 

 over without land connections. 



Getting to the true insects, their mode of dispersal certainly varies a great 

 deal. Whereas butterflies, moths, flies, hymenoptera etc. are known to be storm- 

 driven and eventually carried far, heavy beetles, even if they be properly winged. 



