to render the brief summary of Darwin's thoughts and opinions on the subject in any way complete； it was found necessary to say again much that has often been said before。 No attempt has been made to display as a whole the vast contribution of Wallace； but certain of its features are incidentally revealed in passages quoted from Darwin's letters。 It is assumed that the reader is familiar with the well…known theories of Protective Resemblance； Warning Colours； and Mimicry both Batesian and Mullerian。 It would have been superfluous to explain these on the present occasion； for a far more detailed account than could have been attempted in these pages has recently appeared。 （Poulton； 〃Essays on Evolution〃 Oxford； 1908； pages 293…382。） Among the older records I have made a point of bringing together the principal observations scattered through the note… books and collections of W。J。 Burchell。 These have never hitherto found a place in any memoir dealing with the significance of the colours of animals。
INCIDENTAL COLOURS。
Darwin fully recognised that the colours of living beings are not necessarily of value as colours； but that they may be an incidental result of chemical or physical structure。 Thus he wrote to T。 Meehan； Oct。 9； 1874： 〃I am glad that you are attending to the colours of dioecious flowers； but it is well to remember that their colours may be as unimportant to them as those of a gall； or； indeed； as the colour of an amethyst or ruby is to these gems。〃 （〃More Letters of Charles Darwin〃； Vol。 I。 pages 354； 355。 See also the admirable account of incidental colours in 〃Descent of Man〃 （2nd edition）； 1874； pages 261； 262。）
Incidental colours remain as available assets of the organism ready to be turned to account by natural selection。 It is a probable speculation that all pigmentary colours were originally incidental； but now and for immense periods of time the visible tints of animals have been modified and arranged so as to assist in the struggle with other organisms or in courtship。 The dominant colouring of plants； on the other hand； is an essential element in the paramount physiological activity of chlorophyll。 In exceptional instances； however； the shapes and visible colours of plants may be modified in order to promote concealment。
TELEOLOGY AND ADAPTATION。
In the department of Biology which forms the subject of this essay； the adaptation of means to an end is probably more evident than in any other； and it is therefore of interest to compare； in a brief introductory section； the older with the newer teleological views。
The distinctive feature of Natural Selection as contrasted with other attempts to explain the process of Evolution is the part played by the struggle for existence。 All naturalists in all ages must have known something of the operations of 〃Nature red in tooth and claw〃； but it was left for this great theory to suggest that vast extermination is a necessary condition of progress； and even of maintaining the ground already gained。
Realising that fitness is the outcome of this fierce struggle； thus turned to account for the first time； we are sometimes led to associate the recognition of adaptation itself too exclusively with Natural Selection。 Adaptation had been studied with the warmest enthusiasm nearly forty years before this great theory was given to the scientific world； and it is difficult now to realise the impetus which the works of Paley gave to the study of Natural History。 That they did inspire the naturalists of the early part of the last century is clearly shown in the following passages。
In the year 1824 the Ashmolean Museum at Oxford was intrusted to the care of J。S。 Duncan of New College。 He was succeeded in this office by his brother； P。B。 Duncan； of the same College； author of a History of the Museum； which shows very clearly the influence of Paley upon the study of nature； and the dominant position given to his teachings： 〃Happily at this time （1824） a taste for the study of natural history had been excited in the University by Dr Paley's very interesting work on Natural Theology； and the very popular lectures of Dr Kidd on Comparative Anatomy； and Dr Buckland on Geology。〃 In the arrangement of the contents of the Museum the illustration of Paley's work was given the foremost place by J。S。 Duncan： 〃The first division proposes to familiarize the eye to those relations of all natural objects which form the basis of argument in Dr Paley's Natural Theology； to induce a mental habit of associating the view of natural phenomena with the conviction that they are the media of Divine manifestation； and by such association to give proper dignity to every branch of natural science。〃 （（From 〃History and Arrangement of the Ashmolean Museum〃 by P。B。 Duncan： see pages vi； vii of 〃A Catalogue of the Ashmolean Museum〃； Oxford； 1836。）
The great naturalist； W。J。 Burchell； in his classical work shows the same recognition of adaptation in nature at a still earlier date。 Upon the subject of collections he wrote （〃Travels in the Interior of Southern Africa〃； London； Vol。 I。 1822； page 505。 The references to Burchell's observations in the present essay are adapted from the author's article in 〃Report of the British and South African Associations〃； 1905； Vol。 III。 pages 57…110。）： 〃It must not be supposed that these charms （the pleasures of Nature） are produced by the mere discovery of new objects： it is the harmony with which they have been adapted by the Creator to each other； and to the situations in which they are found； which delights the observer in countries where Art has not yet introduced her discords。〃 The remainder of the passage is so admirable that I venture to quote it： 〃To him who is satisfied with amassing collections of curious objects； simply for the pleasure of possessing them； such objects can afford； at best； but a childish gratification； faint and fleeting； while he who extends his view beyond the narrow field of nomenclature； beholds a boundless expanse； the exploring of which is worthy of the philosopher； and of the best talents of a reasonable being。〃
On September 14； 1811； Burchell was at Zand Valley （Vlei）； or Sand Pool； a few miles south…west of the site of Prieska； on the Orange River。 Here he found a Mesembryanthemum （M。 turbiniforme； now M。 truncatum） and also a 〃Gryllus〃 （Acridian）； closely resembling the pebbles with which their locality was strewn。 He says of both of these； 〃The intention of Nature； in these instances； seems to have been the same as when she gave to the Chameleon the power of accommodating its color； in a certain degree； to that of the object nearest to it； in order to compensate for the deficiency of its locomotive powers。 By their form and colour； this insect may pass unobserved by those birds； which otherwise would soon extirpate a species so little able to elude its pursuers； and this juicy little Mesembryanthemum may generally escape the notice of cattle and wild animals。〃 （Loc。 cit。 pages 310； 311。 See Sir William Thiselton…Dyer 〃Morphological Notes〃； XI。； 〃Protective Adaptations〃； I。； 〃Annals of Botany〃； Vol。 XX。 page 124。 In plates VII。； VIII。 and IX。 accompanying this article the author represents the species observed by Burchell； together with others in which analogous adaptations exist。 He writes： 〃Burchell was clearly on the track on which Darwin reached the goal。 But the time had not come for emancipation from the old teleology。 This； however； in no respect detracts from the merit or value of his work。 For； as Huxley has pointed out （〃Life and Letters of Thomas Henry Huxley〃； London； 1900； I。 page 457）； the facts of the old teleology are immediately transferable to Darwinism； which simply supplies them with a natural in place of a supernatural explanation。〃） Burchell here seems to miss； at least in part； the meaning of the relationship between the quiescence of the Acridian and its cryptic colouring。 Quiescence is an essential element in the protective resemblance to a stoneprobably even more indispensable than the details of the form and colouring。 Although Burchell appears to overlook this point he fully recognised the community between protection by concealment and more aggressive modes of defence； for； in the passage of which a part is quoted above； he specially refers to some earlier remarks on page 226 of his Vol。 I。 We here find that even when the oxen were resting by the Juk rivier （Yoke river）； on July 19； 1811； Burchell observed 〃Geranium spinosum； with a fleshy stem and large white flowers。。。； and a succulent species of Pelargonium。。。so defended by the old panicles； grown to hard woody thorns； that no cattle could browze upon it。〃 He goes on to say； 〃In this arid country； where every juicy vegetable would soon be eaten up by the wild animals； the Great Creating Power； with all…provident wisdom； has given to such plants either an acrid or poisonous juice； or sharp thorns； to preserve the species from annihilation。。。〃 All these modes of defence； especially adapted to a desert environment； have since been generally recognised； and it is very interesting to place beside Burchell's statement the following passage from a letter written by Darwin； Aug。 7； 1868； to G。H。 Lewes； 〃