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Show 2G8 ISLAND LIFE. (PART II, horses, asses, goats, pigs, dogs, and cats, which now run wild in some of the islands. Absence of indigenous Mam?nalia and Amphibia.-As in all other oceanic islands, we find here no truly indigenous mammalia for thouah there is a mouse of the American genus ' b • Hesperomys, which differs somewhat from any known species, we can hardly consider this to be indigenous ; first, because these creatures have been little studied in South America, and there may yet be many undescribed species, and in the second place because even had it been introduced by some European or native vessel, there is ample time in two or three hundred years for the very different conditions to have established a marked diversity in the characters of the species. This is the more probable because there is also a true rat of the Old World genus Mus, which is said to differ slightly from any known species ; and as this genus is not a native of the Ame~ican continents we are sure that it must have been recently introduced into the Galapagos. There can be little doubt therefore that the islands are completely destitute of truly indigenous mammalia; and frogs and toads, the only tropical representatives of the Amphibia, are equally unknown. Reptiles.-Reptiles, however, which at first sight appear as unsuited as mammals to pass over a wide expanse of ocean, abound in the Galapagos, though the species are not very numerous. They consist of land-tortoises, lizards and snakes. The tortoises consist of two peculiar species, Testudo microphyes, found in most of the islands, and T. abingdonii recently discovered on Abingdon Island, as well as one extinct species, T. ephippi·um, found on Indefatigable Island. These are all of very large size, like the gigantic tortoises of the Mascarene Islands, from which, however, they differ in structural characters ; and Dr. Gunther believes that they have been originally derived from the American continent.1 Considering the well known tenacity of life of these animals, and the large number of allied forms which have aquatic or sub-aquatic habits, it is not a very extravagant supposition that some ancestral form, carried 1 Gigantic Land Tortoises Living and Extinct in the collection of the British Museum. By A. C. L. G. Gunther, F.R.S. 1877. CHAP. Xlli.] 'l'IIE GALAPAGOS ISLANDS. out to sea by a flood, was once or twice safely drifted as far ~s th~ Galapagos, and thus originated the races which now Inhabit them. The lizards are five in number; a peculiar species of gecko~ Phyllodactylus galapagensis, and four species of the Amencan famil! Iguanidre. Two of these are distinct species of the. g~nus Lwcephalus, the other two being large, and so :ery d1s~mct as to be classed in peculiar genera, One of these IS aqua~IC and found in all the islands, swimming in the sea at ~orne dist~nce from the shore and feeding on seaweed; the other IS terres. tn. al, and is confined to the four central islands . Th ese were ongmally. described by Mr. Bell as Amblyrhynchu.s cristat~ts and A. subcnstatus; they were afterwards placed in two other genera ~rachycephalus and Oreocephalus (see Brit. Mus. Oatalog1~e of Lizards), while in a recent paper by Dr. Gunther the marme. species . is again classed as Am blyrhynchus, whil~ the terrestnal ~orm IS placed in another genus Conolophus. How these hzards reached the islands we cannot tell. The fac~ that ~hey_ all belong to American genera or families indicates tdh' eu· denvat.w n .f rom that continent' while their b em· g a1 1 Istmct speCies IS a proof that their arrival took place at a remote epoch, under conditions perhaps somewhat different from any which now prevail. It is certain that animals of this order have some means of crossing the sea not possessed by any other land vertebrates, since they are found in a considerable number ~f islands which possess no mammals nor any oth:~ land reptiles; but what those means are has not yet been positively ascertained. It is unusual for oceanic islands to possess snakes, and it is ~herefore somewhat of an anomaly that two species are found m the Galapagos. Both are closely allied to South American forms,. an~ one is hardly different from a Ohilian snake, so that t~ey mdiCate a more recent origin than in the case of the hzards. Snakes it is known can survive a lana time at sea si~ce a living boa-constrictor once reached the 0 island of st: Vmcent fro~ the coast of South America, a distance of two hundred m1~es by the shortest route. Snakes often frequent trees, and m1ght thus be conveyed long distances if carried ou.t |
