388 ORIGIN OF LIFE IN AMERICA 



have varied, and that drift-wood might have been carried to 

 the island from different directions. Great alterations of 

 wind, he thinks, were probable during the Glacial Epoch, so 

 that these two most potent agencies in the accidental trans- 

 port of species may have varied very much during the periods 

 in which the island received its colonists from other countries. 

 Of course, Dr. Wallace* firmly adheres to the belief that all 

 animals and plants found on the island owe their existence 

 there to some means of occasional transport. 



Thirty species of bugs (Hemiptera) have been recorded by 

 Dr. White from St. Helena, of which five have certainly, and 

 one probably, heen introduced. This leaves twenty-six species 

 indigenous to the island. Of the twenty-one genera of Hemip- 

 tera eight are peculiar to St. Helena, but the general 

 distribution of these insects was so little known at the time 

 that Dr. White was unable to trace their affinities, except that 

 most of them have a wide range, and several are known from 

 Miocene deposits. Only one genus (Megarhaphis) has dis- 

 tinctly African affinities. Dr. White f argues from the 

 general aspect of the fauna and flora, from the non-existence 

 of mammals and reptiles, from the large number of endemic 

 species, and from the great depth of the surrounding sea, that 

 St. Helena at no time could have been joined by land with 

 Africa or South America. A careful consideration of all the 

 known facts led him to believe that the colonists did not arrive 

 all in a body, but that colonisation was spread over a con- 

 siderable period. He rejects the theory of a continuous land 

 surface, contending that the fauna and flora arrived from the 

 north in the direction of the Cape Verd islands. Stepping- 

 stones in the shape of islands, now disappeared, may have 

 existed formerly, thus facilitating dispersal, whilst the 

 marine currents were probably reversed. 



Mr. Pickard-CambridgeJ informs us that forty-four species 

 of spiders are known from the island, some of them being also 

 found in Europe, and two in Egypt. The rest are endemic, 

 but most of them show European relationship. In a former 



* Wallace, A. E., " Island Life," pp. 294303. 



t White, F. B., "Hemiptera of St. Helena," pp. 446460. 



J Pickard-Cambridge, 0., " Spiders of St. Helena," p. 210. 



