I hope that the reader will pause before coming to any final and hostile conclusion on the theory of natural selection. It is the facts and views to be hereafter given which have convinced me of the truth of the theory. The reader may consult my 'Origin of Species,' for a general sketch of the whole subject; but in that work he has to take many statements on trust. In considering the theory of natural selection, he will assuredly meet with weighty difficulties, but these difficulties relate chiefly to subjects--such as the degree of perfection of the geological record, the means of distribution, the possibility of transitions in organs, &c.--on which we are confessedly ignorant; nor do we know how ignorant we are. If we are much more ignorant than is generally supposed, most of these difficulties wholly disappear. Let the reader reflect on the difficulty of looking at whole classes of facts from a new point of view. Let him observe how slowly, but surely, the noble views of Lyell on the gradual changes now in progress on the earth's surface have been accepted as sufficient to account for all that we see in its past history. The present action of natural selection may seem more or less probable; but I believe in the truth of the theory, {14} because it collects under one point of view, and gives a rational explanation of, many apparently independent classes of facts.[4] * * * * * {15} CHAPTER I. DOMESTIC DOGS AND CATS. ANCIENT VARIETIES OF THE DOG--RESEMBLANCE OF DOMESTIC DOGS IN VARIOUS COUNTRIES TO NATIVE CANINE SPECIES--ANIMALS NOT ACQUAINTED WITH MAN AT FIRST FEARLESS--DOGS RESEMBLING WOLVES AND JACKALS--HABIT OF BARKING ACQUIRED AND LOST--FERAL DOGS--TAN-COLOURED EYE-SPOTS PERIOD OF GESTATION--OFFENSIVE ODOUR--FERTILITY OF THE RACES WHEN CROSSED--DIFFERENCES IN THE SEVERAL RACES IN PART DUE TO DESCENT FROM DISTINCT SPECIES--DIFFERENCES IN THE SKULL AND TEETH--DIFFERENCES IN THE BODY, IN CONSTITUTION--FEW IMPORTANT DIFFERENCES HAVE BEEN FIXED BY SELECTION--DIRECT ACTION OF CLIMATE--WATER-DOGS WITH PALMATED FEET--HISTORY OF THE CHANGES WHICH CERTAIN ENGLISH RACES OF THE DOG HAVE GRADUALLY UNDERGONE THROUGH SELECTION--EXTINCTION OF THE LESS IMPROVED SUB-BREEDS. CATS, CROSSED WITH SEVERAL SPECIES--DIFFERENT BREEDS FOUND ONLY IN SEPARATED COUNTRIES--DIRECT EFFECTS OF THE CONDITIONS OF LIFE--FERAL CATS--INDIVIDUAL VARIABILITY.