第3章 AN APPRECIATIONBY CHARLES DARWIN(3)

"In the controversy which is being waged amongst Naturalists since the publication of the Darwinian theory of the origin of species, it has been rightly said that no proof at present existed of the production of a physiological species, that is, a form which will not interbreed with the one from which it was derived, although given ample opportunities of doing so, and does not exhibit signs of reverting to its parent form when placed under the same conditions with it.Morphological species, that is, forms which differ to an amount that would justify their being considered good species, have been produced in plenty through selection by man out of variations arising under domestication or cultivation.The facts just given are therefore of some scientific importance, for they tend to show that a physiological species can be and is produced in nature out of the varieties of a pre-existing closely allied one.This is not an isolated case, for I observed in the course of my travels a number of similar instances.But in very few has it happened that the species which clearly appears to be the parent, co-exists with one that has been evidently derived from it.Generally the supposed parent also seems to have been modified, and then the demonstration is not so clear, for some of the links in the chain of variation are wanting.The process of origination of a species in nature as it takes place successively, must be ever, perhaps, beyond man's power to trace, on account of the great lapse of time it requires.But we can obtain a fair view of it by tracing a variable and far-spreading species over the wide area of its present distribution; and a long observation of such will lead to the conclusion that new species must in all cases have arisen out of variable and widely-disseminated forms.It sometimes happens, as in the present instance, that we find in one locality a species under a certain form which is constant to all the individuals concerned; in another exhibiting numerous varieties;and in a third presenting itself as a constant form quite distinct from the one we set out with.If we meet with any two of these modifications living side by side, and maintaining their distinctive characters under such circumstances, the proof of the natural origination of a species is complete; it could not be much more so were we able to watch the process step by step.It might be objected that the difference between our two species is but slight, and that by classing them as varieties nothing further would be proved by them.But the differences between them are such as obtain between allied species generally.Large genera are composed in great part of such species, and it is interesting to show the great and beautiful diversity within a large genus as brought about by the working of laws within our comprehension."But to return to the Zoological wonders of the Upper Amazon, birds, insects, and butterflies are all spoken of by Mr.Bates in his chapter on the natural features of the district, and it is evident that none of these classes of beings escaped the observation of his watchful intelligence.The account of the foraging ants of the genus Eciton is certainly marvellous, and would, even of itself, be sufficient to stamp the recorder of their habits as a man of no ordinary mark.

The last chapter of Mr.Bates' work contains the account of his excursions beyond Ega.Fonteboa, Tunantins--a small semi-Indian settlement, 240 miles up the stream--and San Paulo de Olivenca, some miles higher up, were the principal places visited, and new acquisitions were gathered at each of these localities.In the fourth month of Mr.Bates' residence at the last-named place, a severe attack of ague led to the abandonment of the plans he had formed of proceeding to the Peruvian towns of Pebas and Moyobamba, and "so completing the examination of the Natural History of the Amazonian plains up to the foot of the Andes."This attack, which seemed to be the culmination of a gradual deterioration of health, caused by eleven years' hard work under the tropics, induced him to return to Ega, and finally to Para, where he embarked, on the 2nd June 1859, for England.Naturally enough, Mr.Bates tells us he was at first a little dismayed at leaving the equator, "where the well-balanced forces of Nature maintain a land-surface and a climate typical of mind, and order and beauty," to sail towards the "crepuscular skies" of the cold north.But he consoles us by adding the remark that "three years'