November 28, 1907J 



NA TURE 



77 



account of being illustrated by thirty coloured plates, 

 which are excellent examples of the three-colour pro- 

 cess. Not only are they for the most part good pic- 

 tures of the animals they purport to represent, but 

 they also show in most cases the natural surroundings 

 of the respective species, so far as these can be 

 reproduced with fidelity to nature. Unfortunately, in 

 one instance that has come under our notice the 

 wrong species has been depicted. We refer to the 

 plate of giraffes and zebras facing p. 42, where 

 the animal purporting to be the true or mountain 

 zebra (Equtis zebra) is the northern race of the bonte- 

 quagga, or Burchell's zebra (Eqiius hurcheUi granti). 

 Had the true zebra been depicted, the plate would 

 then have been wrong, as showing a mountain animal 

 0.1 the open plains. The text includes a brief but 

 well-compiled survey of the whole animal kingdom, 

 from Primates to Protozoa, including sporatozoans, 

 with some mention of extinct forms, and the work 

 as a whole appears thoroughly suited to its purpose. 



Precis des Caracteres giniriques des Insectes, dis- 

 poses dans un Ordre naturel par le Citoyen Latreille. 

 A Paris, chez Prevot, Libraire, Ouai des .Augustins, 

 et k Brive, chez F. Bourdeaux, Imprimeur Libraire. 

 .\ Brive, de I'lmprimerie de F. Bourdeaux, an 

 S de la R. [1796]. Pp. xiv + 208. (Imprime a 200 

 Exemplaires par .\. Hermann, n.d.) Price 7 francs. 

 Thi^ is a reprint of a very rare book, which is seldom 

 to be found even in the best entomological libraries. 

 It commences with a table of the fourteen classes into 

 which the author divides insects (understanding by that 

 term .\rachnida, Crustacea, and Myriopoda, as well 

 as Hexapoda), followed by systematic characters for 

 ^ji genera recognised by Latreille, one or two 

 others, de.scribed by other authors, being passed over 

 as at present unknown to him. Several very familiar 

 genera, such as Ypsolophus and Adela, are character- 

 ised in this book for the first time, but without indi- 

 cation of tvpes, for which reference must be made to 

 Latreille's later works. It is always unsatisfactory to 

 entomological authors to be in doubt respecting the 

 actual contents of a book they only know at second- 

 hand, and we are glad that this scarce book has now 

 been rendered accessible to them in a complete (and, 

 we hope, accurate) reprint. 



Tlie Metric and British Systems of Weights, Measures 

 and Coinage. By Dr. F. Molhvo Perkin. Pp. 83 ; 

 with 17 diagrams. (London: Whittaker and Co., 

 H)o7.) Price Js. 6d. 

 Dk. Perkin here provides a simply written and clearly 

 expressed account of metric measures of length, area, 

 volume and weight, and. in addition, treats of specific 

 gravities, temperature measurements, and money. 

 A^ Lord Kelvin has said, " our weights and measures 

 are time-wasting and brain-wearing," and all attempts 

 to familiarise British boys with the simplicity and 

 convenience of the decimal system deserve encourage- 

 ment. This small volume should prove useful in both 

 d.iv and evening schools, and all engaged in manu- 

 facture and commerce would derive advantage from 

 its study. 



The Story of Scraggles (A Sparrow). By George W. 

 James. Illustrated from drawings by Sears Gal- 

 lagher and from photographs. Pp. 88. (London : 

 Cliatto and Windus, 1907.) Price 2s. 6d. 

 The greater part of this booklet is in the form of the 

 autobiographv of an ailing song-sparrow, which could 

 not fly. and was kept in a house for three months. 

 The story, which purports to represent the bird's 

 thoughts and feelings, will probably appeal to little 

 girls, and encourage them to be kind to animals. 

 NO. T987, VOL. 77] 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is talien of anonymous communications.] 



Specific Stability and Mutation. 



Mr. R. H. Lock at the close of his letter in Nature 

 of October 17 (vol. Ixxvi., p. bib) makes a remark which, 

 after some consideration, still perple.\es me. The question 

 involved is so interesting and, indeed, important, that I 

 feel sure that many of your readers would be glad to 

 know the grounds, doubtless not without weight, which led 

 him to it. I quote the passage : — " that natural conditions 

 lead to the obliteration of a host of mutations is as fair a 

 deduction from the fact that such mutations appear under 

 cultivation as the current deduction that the conditions of 

 cultivation actually cause the occurrence of this kind of 

 variation. We have the testimony of de Vries and others 

 that the former process actually takes place. That the 

 latter process does so is an assumption which still lacks 

 the support of facts." 



It contains two propositions : — (1) mutations appear 

 under cultivation ; (2) that the conditions of cultivation 

 actually cause the occurrence of this kind of variation 

 ... is an assumption which still lacks the support of 

 facts. It is the latter on which I think some discussion 

 would probably be illuminating. At first sight the two 

 propositions look contradictory. It is possible, however, 

 that -Mr. Lock is using " cause " in a very technical sense. 

 But as Mill remarks, " in practice that particular con- 

 dition is usually styled the cause, whose share in the 

 matter is superficially the most conspicuous." Now, our 

 knowledge of mutations is almost exclusively drawn from 

 cultivated plants. In such cases cultural conditions are 

 obviously an inseparable antecedent to mutations. What 

 I do not understand is why it is an " assumption " to state 

 that there is a causal nexus between the effect and the 

 conditions. 



To avoid ambiguity, I may explain that by " variation " 

 I mean insensible and continuous organic change ; by 

 "mutation," that which is large, palpable, and discon- 

 tinuous. 



I believe that in nature variation never ceases, and yet 

 " species " do not perceptibly vary. I pointed out some 

 years ago, in a discussion at the Royal Society, the ex- 

 planation of this seeming paradox. What we mean by a 

 species is an abstraction which has no concrete existence. 

 It is the mean or average of a host of varying individuals. 

 It will be hardly contested nowadays that, so long as the 

 conditions remain constant, the species remains unchanged. 

 As has been frequently pointed out, the Egyptian flora 

 furnishes a remarkable illustration of the fact over a 

 long period of time. Plant remains from tombs believed 

 to be 4000 years old differ in no respect from the species 

 now living to which they belong, and the mere fact of 

 their preservation shows that the physical conditions have 

 undergone no change. To this persistence under constant 

 surroundings I have given the name of " specific stability. " 



That mutations occur and exist is obvious to everyone. 

 But that they are of frequent occurrence under purely 

 natural conditions is, I think, unsupported by evidence, 

 and. if they do occur, I agree with Darwin that it may 

 be doubted if they " are ever permanently propagated in 

 a state of nature " (" Origin," fifth edition, p. 4q). The 

 reason is that an organism is so nicelv adjusted to its 

 surroundings that it is in the highest degree improbable 

 that a sudden and extreme structural change would fit in 

 with them. 



If species arise in nature by discontinuous variation or 

 mutation, one would expect to see some evidence of their 

 doing so ; but in the British flora I can only call to mind 

 a very few instances. There is a form of Chelidonium 

 majus with laciniate leaves and petals. It is said to have 

 first appeared at Heidelberg in 1590; according to Hooker 

 it is only known in cultivation. There are two striking 

 mutations of Plantago major, one with a paniculate in- 

 florescence, the other with, leafy bracts, - which reappear 



