CHAP. XIV 



ST. HELENA. 



303 



now found in the Nortli Atlantic islands and Southern 

 Europe ; but it is not at all improbable that they are really- 

 widespread Miocene types, which have been preserved 

 mainly in favourable insular stations. They may there- 

 fore have originally re&^ched St. Helena from Southern 

 Africa, or from some of the Atlantic islands, and may have 

 been conveyed by oceanic currents as well as by winds.-^ 

 This is the more probable, as a large 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 

 larvae 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 

 support 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 type. The other 

 orders of insects have not been collected or studied with 



^ On Petermann's map of Africa, in Sticlers Hand- Atlas (1879), tlie 

 Island of Ascension is shown as seated on a much larger and shallower 

 submarine bank than St. Helena. The 1,000 fathom line round Ascension 

 encloses an oval space 170 miles long by 70 wide, and 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 im- 

 migrants 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 Nahtralist's Voyage Hound the TForld, p. 495.) 



