chap, xiv.] THE NEOTROPICAL REGION. 33 



reptile is a laud tortoise ( Tesiudo nigra) of immense size, and also 

 abundant in all the islands. Its nearest ally is the equally large 

 species of the Mascarene Islands ; an unusual development due, 

 in both cases, to the absence of enemies permitting these slow 

 but continually growing animals to attain an immense age. It 

 is believed that each island has a distinct variety or species of 

 tortoise. 



Insects. — Almost the only insects known from these islands 

 are some Coleoptera, chiefly collected by Mr. Darwin. They 

 consist of a few peculiar species of American or wide ranging 

 genera, the most important being, a Calosoma, Pcecilus, Solen- 

 ophorus, and Notaphus, among the Carabidse ; an Oryctes among 

 the Lamellicornes ; two new genera of obscure Heteromera ; two 

 Curculionidse of wide-spread genera ; a Longicorn of the South 

 American genua Eburia ; and two small Phytophaga, — a set of 

 species highly suggestive of accidental immigrations at rare and 

 distant intervals. 



Land-Shells. — These consist of small and obscure species, 

 forming two peculiar sub-genera of Bulimulus, a genus greatly 

 developed on the whole West coast of America ; and a single 

 species of Bidiminus, a genus which ranges over all the world 

 except America. As in the case of the birds, most of the islands 

 have two or three peculiar species. 



General Conclusions. — These islands are wholly volcanic and 

 surrounded by very deep sea; and Mr. Darwin is of opinion, 

 not only that the islands have never been more nearly con- 

 nected with the mainland than at present, but that they have 

 never been connected among themselves. They are situated 

 on the Equator, in a sea where gales and storms are almost 

 unknown. The main currents are from the south-west, an ex- 

 tension of the Peruvian drift along the west coast of South 

 America. From their great extent, and their volcanoes being 

 now almost extinct, we may assume that they are of consider- 

 able antiquity. These facts exactly harmonize with the theory, 

 that they have been peopled by rare accidental immigrations 

 at very remote intervals. The only peculiar genera consist of 

 birds and lizards, which must therefore have been the earliest 



