344 C. SKOTTSBERG 



size, flight capacity, habits, mode of reproduction, sensitiveness to changes of 

 miUeu, and so forth, and I am afraid that we have httle knowledge, founded on 

 facts, in most cases. 



liarth-iroDus have been carried all over the world with the human traffic. 

 It is noteworthy that as a rule no truly indigenous species are found on oceanic 

 islands, where, if land connections had existed, they could be expected, and even 

 if the transport of eggs or living animals were effected only by means of rafts 

 stocked with earth and plant material, as some believe, they ought to be present, 

 but, as far as I am aware, nobody has witnessed such a transport. The presence 

 of endemic leeches on Samoa and Juan Fernandez (Masafuera) can be understood 

 only if the leeches are carried about on birds acting as hosts, otherwise I cannot 

 see how they would be able to survive; they are very sensitive to exposure. To 

 these in particular I should like to apply what GULICK, without referring to any 

 special group of animals, wrote (z/^. 405): 



How is it possible at all for creatures that would die almost at touch of sea water to 

 precede man by a million years on islands standing solitary in mid-ocean? Are their 

 remote homes really the left-over fragments of ancient inter-continental land bridges, or 

 are these creatures prima facie evidence that their ancestors possessed an almost incon- 

 ceivable capacity for passing uninjured over vast stretches of open ocean? The extremes 

 of hypothesis that have been proposed in response to this dilemma show us how difficult 

 it has been to find a solution. 



Freshwater criistaceaiis occur on many islands, both traffic-borne and indigenous 

 species; only the raft theory would account for their spread. 



It is supposed that cocoons of spiders are transported by wind, webs are 

 torn loose with cocoons attached and carried up into the air, where a storm takes 

 care of them. Theoretically this is not impossible, but whether the contents stand 

 a journey of thousands of miles is doubtful. Adventitious species are found on 

 Pacific islands, but the bulk of the spider faunas is indigenous and endemism is 

 high. Hkki.anI), pointing to the general distribution of genera and the high spe- 

 cific endemism, is in favour of former land connections [2j. 1052). 



L'isolation doit etre assez ancien pour ce que cette fauna ait pu acquerir les carac- 

 tcres d'endemisme (ju'elle presente. Un botaniste a fixe vers le Pliocene cet isolement, 

 mais jc serais porte a croire (pi'il est i)lutc)t ])lus ancien, en me basant sur la lenteur 

 de revolution des Araignees. 



AI.\\R, who rejects all land connections, remarks (27^.214): 



Considering the haj)ha7,ard manner by which these oceanic islands receive their popu- 

 lations, it is rather astonishing how similar the faunas of the various islands are. Ber- 

 i.ANi), on the basis of the distribution of spiders, has come to the conclusion that the 

 fauna of all Polynesia is so uniform as to suggest that these islands are but fragments 

 of a single land mass. This view is similar to Pilsbry's, founded on Mollusca. Actually, 

 this j)aradox of tlie similarity of the fiiunas of oceanic islands is solved in quite dif- 

 ferent manner. Of all the j)Ossil)lc families, genera and species of the Papuan Region 

 that are theoretically in a position to colonize, only a small fraction will eventually 

 avail themselves of the opportunity. 



