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Show 536 SIR V. BROOKE ON THE GENUS GAZELLA. [June 3, Professor Huxley, in dealing with analogous ethnological difficulties, appears to me to obtain with like force in the present instance. Prof. Huxley thus writes * : " I speak of ' persistent modifications ' or * stocks, 'rather than of 'varieties' or 'species,' because each of these last well-known terms implies, on the part of its employer, a preconceived opiuion touching one of those problems the solution of which is the ultimate object of the science." Throughout this paper, however, I shall use the terms " species " and " persistent modification " synonymously, although, for two reasons, the latter term appears to m e infinitely the preferable :-first in that (assuming evolution) it of necessity contains the former, and therefore in being more comprehensive better suits our present uncertainty; and, secondly, in that it points towards a definite biological fact, in favour of which certainly all the evidence as yet collected tends, viz. that the existing forms of Gazella are but modifications, which appear to us persistent, of some as yet unknown extinct Artiodactyle form. At the close of my paper I shall again allude to this subject, and shall endeavour to indicate the manner in which I conceive it possible to account for the present modifications and distribution of the group. For the sake of convenience, and the avoidance of constant repetition, and also to throw into relief the traces of genetic affinity afforded by coloration, I will describe the typical ground-plan which may be seen underlying each variation, the uniformity of the arrangement of the more salient and characteristic markings (where they appear) throughout the group clearly showing the existence of such a plan. To each of these more prominent features, indicating what may be provisionally called genetic coloration, I will apply a definite name which I shall make use of in the following descriptions. The anterior facial region in Gazelles, from the base of each horn to the muzzle, is cut off from the sides of the face on both sides by white streaks, which, starting externally to the base of each horn, run downwards to within 2 inches of the nostrils ; the former I shall call the central facial band, the latter the light facial streaks. From the corner of the suborbital gland, running downwards immediately below the light facial streak, and of about equal width, is a dark line ; this I shall refer to as the dark facial streak. Bordering the white of the belly on each side, and extending from above and behind the ulna, to above and in front of the patella, are two bands, the lower of which is darker, the upper lighter than the colour of the back and flanks. The former I shall speak of as the dark, the latter the light lateral band. Lastly, bordering the white of the rump is frequently seen a narrow indefinite darkish band, which may be conveniently called the pygal band. The difficulty of expressing differences dependent to a large extent upon shades of colour and texture of hair sufficiently sharply to give a just impression of the effect produced by such differences upon the eye, may cause the distinction of some of the forms below mentioned to appear doubtful. I can only say that upon occasions when I have had ample opportunity of subsequently verifying * Critiques and Addresses, p. 134. |