330 



NATURE 



\_AMg. 17, 1876 



An accurate observer related to me the case of a lady whose 

 iris changed colour in bright sunlight. 



These few instances seem to show that the behaviour and 

 properties of pigment-cells are independent of the protective 

 functions for which they have, in some cases, been specialised 

 and augmented by the action of natural selection. 



It seems a pity that Mr, Murphy should write on a question in 

 natural history without making himself better acquainted with 

 what is known on the subject. Francis Darwin 



Down, Beckenham, Aug. 14 



In the last number of Nature Mr. J. J. Murphy states the 

 difficulty which he finds in accounting for the rise of inter- 

 mittent variations upon the theory of natural selection. He can 

 understand the origin of a white species from a brown one or 

 vice vend, but not of a species which, like the ermine, is at one 

 season brown and at another season white. He speaks of "facts 

 of colour which it seems impossible for natural selection to 

 produce, from the infinite improbability of a first variation ever 

 occurring." From this mode of expression one might fancy that 

 Mr. Murphy had for the moment forgotten that natural selec- 

 tion is in no way concerned with producing, but acts only by 

 preserving, variations. As in a great number of instances we are 

 Ignorant of the precise antecedents which produce variation, 

 whether chronic or recurrent, in such instances, we must be left 

 at liberty, if we choose, to invoke the special action of "a 

 guiding intelligence." The case, however, of an animal which 

 changes its colour with the season does not seem to be one of 

 very exceptional difficulty. It is only necessary to suppose that 

 the animal became possessed of pigments liable to be acted 

 on in the required direction by the seasonal changes of light 

 and heat. It might well be that with some animals the influ- 

 ence of the same changes would be in a direction just the oppo- 

 site of what was useful to them. In thatcase the variety would 

 stand but little chance of being preserved. Similar explana- 

 tions hold with regard to the vegetable kingdom. I have 

 now before me drawings of Sempcrmvum spinoitim. The 

 summer rosette is bright green in colour, with the leaves 

 expanded, while the winter rosette is a compact little 

 ball of a dull purple. Thus the plant prepares itself against 

 the cold of winter and the dearth of nourishment which that 

 season brings, but it is likely enough that cold and dearth in the 

 first instance led to the variation in the plant from its summer 

 habit. 



In human beings the hair is said sometimes to turn white from 

 sudden grief or terror. Liability to such a change does not 

 probably carry any such advantage to the human species as 

 would make it likely to spread and develop itself further. But 

 in the little shrimp commonly known as Mysis chamccleon, we 

 can at least conjecture that a very solid advantage might follow 

 from a similar characteristic. I have sometimes bottled live 

 sjiecimens of this little creature while it was of a dark purple 

 colour, and presently after lost sight of it, the fact proving to be 

 upon closer inspection that it had become almost completely 

 transparent. Among its ordinary enemies the loss of colour 

 might often save its life, in which case natural selection would 

 tend to preserve the aptitude, although the aptitude itself, like 

 the bleaching of human hair from grief, has no connection at the 

 outset with the advantage of the species. 



Torquay, Aug. 14 Thomas R. R. Stebbing 



Mr. Murphy's letter (Nature, vol. xiv. p. 309) opens up a 

 wide field for speculation. The class of cases to which he 

 directs attention constitutes what I have designated ^* variable 

 protective colouring," and in a paper communicated to the 

 Zoological Society (Proc. Zoo. Soc, 1872), I attempted to 

 show that such cases came to a certain extent within the scope 

 of natural selection. The line of argument pursued is briefly as 

 follows : — Natural selection, working solely for the good of a 

 species takes advantage of all beneficial variations, no matter 

 how they may originate. In but very few cases can the cause of 

 any particular variation be assigned. Natural selection works 

 only on the variations presented to it, the causes of such varia- 

 tions appearing to us, in the absence of observational or experi- 

 ipental evidence, mysterious. If, then, a species deriving advan- 

 tage from protective colouring under one set of conditions, finds 

 that the conditions vary periodically or irregularly, thus rendering 

 that mode of colouring useless or even disadvantageous, it clearly 

 becomes advantageous to the species to possess a power of adapta- 

 tion. By this means only can vaiying external conditions he 



met, and it is upon this adaptive power that I venture to think 

 the action of natural selection has in these cases been exerted. 

 That the particular cause of such variation cannot be assigned, 

 no more weakens thi natural selection argument in these cases 

 than in ordinary instances of permanent protective colouring, 

 the possibility of which having been brought about by the 

 '* survival of the fittest," Mr. Murphy seems disposed to admit. 



One argument in favour of the natural selection theory of pro- 

 tective colouring appears, so far as I am aware, to have been 

 overlooked. It has been urged that granting the power of 

 natural selection to produce a general resemblance in colour, 

 &c., to inanimate objects, it is difficult to see how the highly 

 perfect finishing touches (instances of which are familiar to all 

 naturalists) could have been imparted by this same agency. To 

 thi? it may be replied that the marvellously perfect resemblances 

 which we witness have not been brought about to deceive our 

 visual sense, but that of far keener-sighted foes whose very 

 means of subsistence may depend upon acuteness of vision. 



Aprvpos of Mr. Power's letter in the same number of Nature, 

 I have recently had an opportunity of observing how closely the 

 larva of Trachea piniperda resembles in the longitudinal green 

 stripes the needle-shaped leaves of the pine on which it feeds. I 

 observed also an equally good adaptation in a larva of Agriopis 

 aprilina, which when resting on a lichen-covered oak trunk was 

 barely discernible from the lichen on which it rested. 



Belle Vue, Twickenham, Aug. 12 R. Meldola 



Antedated Books 



The grievance pointed out by your correspondent " F.Z.S." 

 is a real one. Nevertheless I trust that the writer is himself free 

 from the charge that he so glibly brmgs against a brother natu- 

 ralist of endeavouring to obtain for his generic titles an " unjust 

 priority of fifteen months over what they are entitled to." I am 

 sorry that there should be a Fellow of the Zoological Society 

 who believes me capable of doing this, but, as the charge has 

 been thus publicly made, I lose no time in flinging it back upon 

 my anonymous accuser. The new edition of Layard's "Birds 

 of South Africa " was announced to appear in six parts, and the 

 first was published in May, 1875. The number of wrappers 

 required for the six parts was printed off at the time, and 

 "F.Z.S." will find that Part 2, which was published last autumn 

 has precisely the same wrapper as Part i, and this is the case 

 with the part now issued. I admit that it would have been 

 belter to have altered the date on each wrapper in writing ; but 

 this, probably, did not occur to my publisher, who is doubtless 

 not aware of the importance attached to the law of priority by 

 " F.Z.S.," your correspcndent, who, apparently, in his hurry to 

 attribute an unworthy motive, has scarcely taken the trouble to 

 look beyond the, cover of the book. Had he done so he might have 

 been satisfied that the letterpress contained abundant evidence 

 of having been written long after the date which he would have 

 the scientific world believe I had endeavoured to claim for its 

 publication. Such an attempt would be absurd when docu- 

 ments are quoted in the letterpress which were not in existence in 

 the year 1875. 



May I at the same time reply to a paragraph of your reviewer 

 (p. 318) on the "Birds of Kerguelen Island." This pamphlet 

 deserves all the praise which the reviewer bestows on it, 

 but in his endeavour to disparage his own countrymen, and 

 to trumpet the superior energy of American ornithologists, 

 he seems to have done an injustice to Mr. Eaton and myself. 

 Two new species were mentioned by Dr. Coues, viz., ^strelata 

 kidderi, which Mr. Salvin {Orn. Misc., p. 235) shows to be 

 ^. brevirostrts (Less. ), and secondly, Querquedula eateni (Sharpe). 

 This latter name looks as if the English ornithologists had not 

 been so far behind their American brethren, after all, if the 

 description of the new Teal was available for quotation in Dr. 

 Coues' work ! R. Bowdler Sharpe 



British Museum 



Fully agreeing with "F.Z.S." in reprobating the evil 

 practice of which he complains, I think that in the particular 

 instance he cites, of the recently published third part of the new 

 edition of "The Birds of South Africa," he will, on looking 

 again at its wrapper, see that the information it affords is so 

 contradictory as to be worth nothing. The first words upon it 

 are "To be completed in Six Parts ;'" but on its second page 

 we read that the publisher "has decided upon issuing this work 

 in y^iz^r parts !" Which of these statements is to be believed? 

 In justice to the publisher, however, it is to be observed that the 

 number " 3 " is not printed, but inserted with the pen, in the 



