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 The observations of Spruce are of themselves almost conclusive as to the possibility of Europeans becoming acclimatized in the tropics; and if it is objected that this evidence applies only to the dark-haired southern races, we are fortunately able to point to facts, almost equally well authenticated and conclusive, in the case of one of the typical Germanic races. In South Africa the Dutch have been settled and nearly isolated for over 200 years, and have kept themselves almost or quite free from native intermixture. They are still preponderatingly fair in complexion, while physically they are tall and strong. They marry young and have large families. The population, according to a census taken in 1798, was under 22,000. In 1865 it was near 182,000, the majority being of “Dutch, German or French origin, mostly descendants of original settlers.” In more recent times, the conditions have been so greatly changed by immigration, that the later statistics cease to have a definite meaning with regard to acclimatization. We have here a population which doubled itself every twenty-two years; and the greater part of this rapid increase must certainly be due to the old European immigrants. In the Moluccas, where the Dutch have had settlements for 250 years, some of the inhabitants trace their descent to early immigrants; and these, as well as most of the people of Dutch descent in the east, are quite as fair as their European ancestors, enjoy excellent health, and are very prolific. But the Dutch accommodate themselves admirably to a tropical climate, doing much of their work early in the morning, dressing very lightly, and living a quiet, temperate and cheerful life. They also pay great attention to drainage and general cleanliness. In addition to these examples, it is obvious that the rapid increase of English-speaking populations in the United States and in Australia is far greater than can be explained by immigration, and shows two conspicuous examples of acclimatization.

On the whole, we seem justified in concluding that, under favourable conditions, and with a proper adaptation of means to the end in view, man may become acclimatized with at least as much certainty and rapidity (counting by generations rather than by years) as any of the lower animals. The greatest difficulty in his way is not temperature, but the presence of parasitic diseases to resist which his body has not been prepared, and modern knowledge is rapidly defining these dangers and the modes of avoiding them.

The task of collecting information as to animals which have become permanently naturalized away from their native haunts is anything but easy, as few regular records have been kept by acclimatizers. Moreover, recorders of local fauna have been almost unanimous in ignoring the introduced forms, except when they have had occasion to comment on the effects, real or supposed, of these immigrants on aboriginal faunas.

Mammals.—It is unnecessary here to dwell upon the world-wide distribution of the two rats Mus rattus and M. decumanus, and of the house-mouse M. musculus; their introduction has always been involuntary. Similarly nearly all our domestic mammals except the sheep have become feral somewhere or other, whether by intentional liberation or by escape; but the smaller ones more than the larger, such as pigs, goats, dogs and cats. This has been especially the case in Hawaii and New Zealand; in America, Australia and Hawaii, horses and cattle are also feral. Feral pigs are numerous in New Zealand.

The domestic Indian buffalo (Bos bubalus) exists as a wild animal in North Australia; it is very liable to revert to a wild state, being little altered from its still-existing wild ancestor. A more curious case is that of the one-humped camel (Camelus dromedarius), a beast only known in domestication, and that in arid countries; yet a number of these have become feral in the Spanish marshes, where they wade about like quadrupedal flamingoes.

The red deer (Cervus elaphus) is now widely distributed as a wild animal over New Zealand, where also the fallow-deer (C. dama) and the Indian sambar (C. aristotelis or unicolor) have been introduced locally. The sambar, or one or other of its subspecies, has also been naturalized in Mauritius, and in the Marianne Islands in the open Pacific.

The wide introduction of the rabbit, as a wild animal, is well known. Amounting to a serious pest in Australasian colonies, it is also established in the Falklands and Kerguelen; its presence in much of Europe is attributed to early acclimatization, as it seems anciently to have been confined to the Iberian peninsula.

The hare has been established in New Zealand and Barbadoes. Few other rodents have been designedly naturalized, but the North American grey squirrel (Sciurus cinereus) appears to be established as a wild animal in Woburn Park, Bedfordshire, England, and may probably spread thence.

To check the increase of the rabbit, stoats, weasels and polecats (the last in the form of the domesticated ferret) were introduced into New Zealand on a very large scale in the last quarter of the 19th century. They have spread widely, and have not confined their depredations to the rabbits, so that the indigenous flightless birds have suffered largely.

Another carnivore of very similar habits, the Indian mongoose (Herpestus griseus or H. mungo), has been naturalized in Jamaica, whence it has been carried to other West Indian Islands, and in the Hawaiian group. It has also been tried, but unsuccessfully, in Australia. The first introduction into Jamaica took place in 1872, and ten years later the animal was credited with saving many thousands of pounds annually by its destruction of rats. But before an equal space of time had further elapsed, it had itself become a pest; the most recent information, however, is to the effect that its numbers are now on the decline, and that the disturbed faunal equilibrium is being readjusted.

The civets, being celebrated for their odoriferous secretion, are likely animals to have been naturalized. W. T. Blanford (Fauna of British India, “Mammals”) thinks that the presence of the Indian form, Viverricula malaccensis, in Socotra, the Comoro Islands and Madagascar is due to the assistance of man.

The common fox of Europe has been introduced into Australia, where it is destructive to the native fauna and to lambs.

Among primates, a Ceylonese monkey (Macacus pileatus) has been naturalized in Mauritius for centuries, the circumstances of introduction being unknown.

The common Australian “opossum” or phalanger (Trichosurus vulpecula) has been naturalized in New Zealand, although very destructive to fruit trees; the value of its fur being probably the motive. It is said that the pelage of the New Zealand specimens is superior, as might be expected from the colder climate.

Birds.—The introduction of mammals has been largely influenced by economic conditions, when, indeed, it was not absolutely accidental and unavoidable; but in the case of birds it has been more gratuitous, so to speak, in many cases, and hence is looked upon with especial dislike by naturalists. The domestic birds have comparatively seldom become feral, doubtless, as C. Darwin points out, from the reduction of their powers of flight in many cases. The guinea-fowl, however, has long been in this condition in Jamaica and St Helena, and the fowl in Hawaii and other Polynesian islands. The pheasant has been naturalized in the United States, New Zealand, Hawaii and St Helena. Its naturalization in western Europe is very ancient, but the race supposed to have been introduced by the Romans (Phasianus colchicus) has been much modified within the last century or two by the introduction of the ring-necked Chinese form (P. torquatus), which produces fertile hybrids with the old breed. Thus those acclimatized were usually, no doubt, of mixed blood, and further introductions of pure Chinese stock have tended to make the latter the dominant form, at any rate in the United States (where it is erroneously called Mongolian ) and in New Zealand. In Hawaii and St Helena the ring-neck appears to have been the only pheasant introduced pure, but in the former the Japanese race (P. versicolor) is also naturalized.