292 



ISLAND LIFE. 



[part II.' 



proportion of the St. Helena beetles live even"_in the perfect state 

 within the stems of plants or trunks of trees, while the eggs 

 and larvse of a still larger number are likely to inhabit similar 

 stations. Drift-wood might therefore be one of the most 

 important agencies by which these insects reached the island. 



Let us now see how^ far the distribution of other groups sup- 

 port the conclusions derived from a consideration of the beetles. 

 The Hemiptera have been studied by Dr. F. Buchanan White, 

 and though far less known than the beetles, indicate somewhat 

 similar relations. Eight out of twenty-one genera are peculiar, 

 and the thirteen other genera are for the most part widely 

 distributed, while one of the peculiar genera is of African tj^pe. 

 The other orders of insects have not been collected or studied 

 with sufficient care to make it worth while to refer to them 

 in detail ; but the land-shells have been carefully collected and 

 minutely described by Mr. Wollaston himself, and it is interest- 

 ing to see how far they agree with the insects in their 

 peculiarities and affinities. 



Land-shells of St. Helena. — The total number of species is 

 only twenty-nine, of which seven are common in Europe or the 

 other Atlantic islands, and are no doubt recent introductions. 

 Two others, though described as distinct, are so closely allied to 

 European forms, that Mr. Wollaston thinks they have probably 



even the 300 fathom line, one over 60 miles long ; and it is therefore 

 probable that a much larger island once occupied this site. Now Ascension 

 is nearly equidistant between St. Helena and Liberia, and such an island 

 might have served as an intermediate station through which many of the 

 immigrants to St. Helena passed. As the distances are hardly greater 

 than in the case of the Azores, this removes whatever difficulty may have 

 been felt of the possibility of any organisms reaching so remote an island. 

 The present island of Ascension is probably only the summit of a huge 

 volcanic mass, and any remnant of the original fauna and flora it might 

 have preserved may have been destroyed by great volcanic eruptions. Mr. 

 Darwin collected some masses of tufa which were found to be mainly 

 organic, containing, besides remains of fresh-water infusoria, the siliceous 

 tissue of plants ! In the light of the great extent of the submarine bank 

 on which the island stands, Mr. Darwin's remark, that— ''we may feel 

 sure, that at some former epoch, the climate and productions of Ascension 

 were very different from what they are now,"— has received a striking 

 confirmation. (See Naturalist's Voyage Round the World, p. 495.) 



