B88 
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, been 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-Cambridge^ 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. R., “ Island Life,” pp. 294—303. 
t White, F. B., “Hemiptera of St. Helena,” pp. 446 — 460. 
f Pickard-Cambridge, O., “Spiders of St. Helena,” p. 210. 
