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f 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； 〃That Natural Selection would tend to produce the most formidable thorns will be admitted by every one who has observed the distribution in South America and Africa （vide Livingstone） of thorn… bearing plants； for they always appear where the bushes grow isolated and are exposed to the attacks of mammals。 Even in England it has been noticed that all spine…bearing and sting…bearing plants are palatable to quadrupeds； when the thorns are crushed。〃 （〃More Letters〃； I。 page 308。）
ADAPTATION AND NATURAL SELECTION。
I have preferred to show the influence of the older teleology upon Natural History by quotations from a single great and insufficiently appreciated naturalist。 It might have been seen equally well in the pages of Kirby and Spence and those of many other writers。 If the older naturalists who thought and spoke with Burchell of 〃the intention of Nature〃 and the adaptation of beings 〃to each other； and to the situations in which they are found；〃 could have conceived the possibility of evolution； they must have been led； as Darwin was； by the same considerations to Natural Selection。 This was impossible for them； because the philosophy which they followed contemplated the phenomena of adaptation as part of a static immutable system。 Darwin； convinced that the system is dynamic and mutable； was prevented by these very phenomena from accepting anything short of the crowning interpretation offered by Natural Selection。 （〃I had always been much struck by such adaptations （e。g。 woodpecker and tree…frog for climbing； seeds for dispersal）； and until these could be explained it seemed to me almost useless to endeavour to prove by indirect evidence that species have been modified。〃 〃Autobiography〃 in 〃Life and Letters of Charles Darwin〃； Vol。 I。 page 82。 The same thought is repeated again and again in Darwin's letters to his friends。 It is forcibly urged in the Introduction to the 〃Origin〃 （1859）； page 3。） And the birth of Darwin's unalterable conviction that adaptation is of dominant importance in the organic world；a conviction confirmed and ever again confirmed by his experience as a naturalistmay probably be traced to the influence of the great theologian。 Thus Darwin； speaking of his Undergraduate days； tells us in his 〃Autobiography〃 that the logic of Paley's 〃Evidences of Christianity〃 and 〃Moral Philosophy〃 gave him as much delight as did Euclid。
〃The careful study of these works； without attempting to learn any part by rote； was the only part of the academical course which； as I then felt and as I still believe； was of the least use to me in the education of my mind。 I did not at that time trouble myself about Paley's premises； and taking these on trust； I was charmed and convinced by the long line of argumentation。〃 （〃Life and Letters〃； I。 page 47。）
When Darwin came to write the 〃Origin〃 he quoted in relation to Natural Selection one of Paley's conclusions。 〃No organ will be formed； as Paley has remarked； for the purpose of causing pain or for doing an injury to its possessor。〃 （〃Origin of Species〃 （1st edition） 1859； page 201。）
The study of adaptation always had for Darwin； as it has for many； a peculiar charm。 His words； written Nov。 28； 1880； to Sir W。 Thiselton… Dyer； are by no means inapplicable to…day： 〃Many of the Germans are very contemptuous about making out use of organs； but they may sneer the souls out of their bodies； and I for one shall think it the most interesting part of natural history。〃 （〃More Letters〃 II。 page 428。）
PROTECTIVE AND AGGRESSIVE RESEMBLANCE： PROCRYPTIC AND ANTICRYPTIC COLOURING。
Colouring for the purpose of concealment is sometimes included under the head Mimicry； a classification adopted by H。W。 Bates in his classical paper。 Such an arrangement is inconvenient； and I have followed Wallace in keeping the two categories distinct。
The visible colours of animals are far more commonly adapted for Protective Resemblance than for any other purpose。 The concealment of animals by their colours； shapes and attitudes； must have been well known from the period at which human beings first began to take an intelligent interest in Nature。 An interesting early record is that of Samuel Felton； who （Dec。 2； 1763） figured and gave some account of an Acridian （Phyllotettix） from Jamaica。 Of this insect he says 〃THE THORAX is like a leaf that is raised perpendicularly from the body。〃 （〃Phil。 Trans。 Roy。 Soc。〃 Vol。 LIV。 Tab。 VI。 page 55。）
Both Protective and Aggressive Resemblances were appreciated and clearly explained by Erasmus Darwin in 1794： 〃The colours of many animals seem adapted to their purposes of concealing themselves either to avoid danger； or to spring upon their prey。〃 （〃Zoonomia〃； Vol。 I。 page 509； London； 1794。）
Protective Resemblance of a very marked and beautiful kind is found in certain plants； inhabitants of desert areas。 Examples observed by Burchell almost exactly a hundred years ago have already been mentioned。 In addition to the resemblance to stones Burchell observed； although he did not publish the fact； a South African plant conc