CHAP. XIV 



ST. HELENA 



301 



time for the modification of the originally introduced 

 species, and their special adaptation to the conditions pre- 

 vailing in this remote island. This antiquity is also shown 

 by the remarkable specific modification of a few types. 

 Thus the whole of the Cossonidae may be referred to three 

 types, one species only {Hexacoptus fcrruginmi) being allied 

 to the European Cossonidae though forming a distinct 

 genus ; a group of three genera and seven species remotely 

 allied to the Stenoscelis hylastoides, which occurs also at the 

 Cape ; while a group of twelve genera with forty-six species 

 have their only (remote) allies in a few insects widely 

 scattered in South Africa, New Zealand, Europe, and the 

 Atlantic Islands. In like manner, eleven species of Bem- 

 bidium form a group by themselves ; and the Heteromera 

 form two groups, one consisting of three genera and species 

 of Opatridse allied to a type found in Madeira, the other, 

 Anthicodes, altogether peculiar. 



Now each of these types may well be descended from a 

 single species which originally reached the island from some 

 other land ; and the great variety of generic and specific 

 forms into which some of them have diverged is an indica- 

 tion, and to some extent a measure, of the remoteness of their 

 origin. The rich insect fauna of Miocene age found in 

 Switzerland consists mostly of genera which still inhabit 

 Europe, with others which now inhabit the Cape of Good 

 Hope or the tropics of Africa and South America ; and it 

 is not at all improbable that the origin of the St. Helena 

 fauna dates back to at least as remote, and not improbably 

 to a still earlier, epoch. But if so, many difficulties in 

 accounting for its origin will disappear. We know that 

 at that time many of the animals and plants of the tropics, 

 of North America, and even of Australia, inhabited 

 Europe ; while during the changes of climate, which, as 

 we have seen, there is good reason to believe periodically 

 occurred, there would be much migration from the tem- 

 perate zones towards the equator, and the reverse. If, 

 therefore, the nearest ally of any insular group now in- 

 habits a particular country, we are not obliged to suppose 

 that it reached the island from that country, since we 

 know that most groups have ranged in past times over 



