Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle, Vol. 3 [of 3] · Charles Darwin
ADDENDA.
In another place, Dr. Ferguson says, “It is from these (the dried and half-dried margins of lakes and marshes) that the poison uniformly emanates, and never from the body of the lake or pool; and I think it may be fairly presumed, that water, as long as it can preserve the figure of its particles above the surface, is innoxious, and that it must first be absorbed into the soil, and disappear from the eye, before it can produce any mischievous effects. Whoever in malarious countries waits for the evidence of putrefaction will, in all the most dangerous places, wait too long, as every one can testify who has seen pestilence teem forth, to the paralyzation of armies,--from the bare barren sands of the Alentejo in Portugal, the arid burnt plains of Estremadura in Spain, and the recently flooded table-lands of Barbadoes.” I cannot forbear quoting here a remarkable fact, mentioned by Humboldt, though interpreted in a different manner by that illustrious traveller. Speaking of the intermittent fevers which are so common near the great cataracts, or _raudales_, of the Orinoko, he says (_Pers.
Nar._, vol. v., p. 17) the causes “are violent heats, joined with the excessive humidity of the air, bad nutriment, and, if we may believe the natives (as well as the missionaries), the pestilent exhalations that arise from the bare rocks of the _raudales_.” Further on (p. 85), he says, “many examples are adduced of persons, who having passed the night on these black and naked rocks, have awakened in the morning with a strong paroxysm of fever.” Humboldt thinks that these cases may be explained by the effect produced on the body by the high temperature, which the black rocks, coated with a layer of the oxides of manganese and iron, retain during the night. But it appears to me that the relation is too remarkable to be thus explained, between this fact and those mentioned by Dr. Ferguson, in which the desiccation of nearly bare rock in Spain, and of a very thin bed of earth overlying dry coral rock in the West Indies, has given rise to the most pestiferous exhalations. Page 461. The sixth bird, mentioned as an inhabitant of the Galapagos, Mr. Gould now finds is not like the rest, peculiar to these islands, but is a known North American species of Ammodramus. Page 465.
I have given my reason for believing that the _Testudo_, inappropriately called _Indicus_, is an aboriginal species of the Galapagos. I now find (_Kerr’s Voyages_, vol. x., p. 373) that as far back as 1708, Woods, Rogers, and Courtney, in their voyage round the world, speaking of the tortoises of these islands, say that it is the opinion of the _Spaniards_ that there is no other in _these seas_, except at the Galapagos: it is, however, then added, that they are common in Brazil,--a mistake which may be attributed to two different species not having been distinguished. It has been said that the bones of _Testudo Indicus_ were found in numbers in the Isle of France, with some fragments of those of the Dodo; but M. Bibron--one of the best authorities in Europe on reptiles--informs me that he has reason to believe that a second species has been confounded under this name.
In the same page I remark that there is every reason for believing that several of the islands possess their own peculiar varieties or species of tortoise, but that my specimens were too small to decide this question. M. Bibron now informs me, that he has seen full-grown animals, brought from this Archipelago, which he considers undoubtedly to be distinct species. At p. 467, I have observed that the specimens of the _Amblyrhyncus cristatus_--that extraordinary marine herbivorous lizard--were larger from Albemarle, than from any other island. In this case, also, M. Bibron tells me, he has seen what he considers two species of the aquatic Amblyrhyncus, besides the terrestrial species. Doubtless the several islands have their own representatives of the Amblyrhyncus, like they have of some of the birds, and of the tortoises. With respect to the plants from this Archipelago, Professor Henslow writes to me, that although he has not yet examined them attentively, he finds that “there are several instances of distinct species of the same genus, sent from one island only: that is, whilst the genus is common to two or three islands, the species are often different in the different islands. In some cases the species seem to run very close to each other, but are, I believe, _distinct_.” I may observe that, from my ignorance of botany, I collected more blindly in this department of natural history than in any other; so that certainly it was not _intentionally_ that I brought the different species from different islands. If, indeed, I at all noticed their resemblance, I probably collected the second and third species as duplicate specimens of the first. It is useless to repeat here my regrets at not having procured a perfect series in every order of nature from the several islands: my excuse must be, the entire novelty of the fact, that islands in sight of each other should be characterized by peculiar faunas: I ought, perhaps, rather to think it fortunate, that sufficient materials were obtained to establish so remarkable a circumstance in the geographical distribution of organic beings, although they are insufficient to determine to what extent the fact holds good.
Page 477. To the two cases of land-birds being extremely tame in islands only lately inhabited by man, I might have added Tristan da Acunha. Captain D. Carmichael (_Linn. Transact._, vol. xii., p. 496), speaking of the thrush and bunting--the only true land-birds--says, “they fly about the cantonment, and are so tame as to suffer themselves to be caught with a hand-net.” Page 552. One of the species of Millepora, which is mentioned as having the property of stinging, is the _M. complanata_; and the other, I believe, is _M. alcicornis_. In the Voyage of the Astrolabe (vol. iv., p. 19), an Actinia is said to have this property, and even to infect the water, which it squirts from its mouth. A flexible coralline, allied to Sertularia, was observed (p. 337) at New Ireland to have the same stinging power.
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