October 3, 1912] 



NATURE 



135 



evidence. For instance, with reference to the jaw 

 under discussion Pengelly adds the remark, "Nothing 

 of the kind was subsequently met with in or under the 

 Granular Stalagmite" i}.oc. cit., p. 221). 



A. R. Hunt. 

 Torquay, September 16. 



Mr. Hunt is under a misapprehension regarding 

 mv criticism of Prof. Boyd Dawkins's communication 

 at the Anthropological Section of the British Asso- 

 ciation at Dundee. In making the important an- 

 nouncement that the remains of Neanderthal man !iad 

 been discovered in England, Prof. Dawl-cins exhibited 

 merely a rough sketch of a fragment of a human jaw 

 — not the actual specimen itself. So far as the sketch 

 went it showed none of the usual Neanderthal char- 

 acters. Further, he was unable to say from which 

 stratum of the floor of Kent's Cavern the original 

 specimen had been derived. Mv criticism of " ridicu- 

 lous " and " unscientific " applies merely to the fact 

 that the meeting was asked to accept the discovery 

 of Neanderthal man in England on a specimen which 

 was absent and of uncertain origin. From Mr. 

 Hunt's communication it is clear that the exact origin 

 of the specimen could have been ascertained. I firmly 

 believe that the remains of Neanderthal man will be 

 discovered in England — it may be that Dr. Duck- 

 worth is right regarding the specimen from Kent's 

 Cavern — but the discovery cannot be accepted unless 

 the evidence is produced. A. Keith. 



EXPERIMENTAL RESEARCHES ON 



VARIATIONS IN THE COLOURING OF 



LEPID0PTERA.1- 



THIS is a very comprehensive treatise by Dr. 

 Pictet, a former treatise by whom on a 

 cognate subject was reviewed in Nature in 1905 

 (vol. Ixxii., p. 632). It begins with a resume of 

 previous researclies by various authors, classified 

 under several heads, and proceeds to describe tlie 

 author's own researches and the conclusions he 

 draws from them. Many of the details are highly 

 interesting, and his observations upon them are of 

 much weight. 



Lepidoptera, Dr. Pictet tells us, with few excep- 

 tions, vary in only two directions, melanism and 

 albinism ; the law laid down by Oberthur may be 

 thus summed up : .'\ny part of the wing of a 

 butterfly can become separately darker or lighter 

 than it is normally ; in the former case, whatever 

 its colour (except green) it can darken sufficiently 

 to become brown, and even of so deep a brown 

 as to have the appearance of blackness, leading 

 in all the parts so darkened to melanism ; in the 

 latter case these same parts can become lighter, 

 sufficiently to become tawny (fauve), yellow, and 

 even of a yellow so pale as to appear white, lead- 

 ing, in like manner, to albinism. 



The dark markings of the wing can spread or 

 be displaced, or merge in neighbouring parts, or 

 mask them more or less completely, or they can 

 contract, become partly effaced, or even disappear, 



1 "Recherches Exp^rimentales sur les Mecanismes du M^'anisme et 

 I'Albinisme chez les Lipidopteres." By Dr. Arnold Pictet. Miraoires de 

 la Soci^ttf de Physique et d'Histoire naturelle de Geneve, vol. xxxvii. 

 Pp. 111-278 + S plates. (Geneve: George & Cie. ; Paris: G. Fischbacher. 

 S912.) 



NO. 2240, VOL. go] 



giving place to the light markings of the ground 

 colour (fond). In other cases certain markings 

 may become darker, and others lighter, or the 

 general colour may become darker or lighter with- 

 out altering the pattern. Opposite exciting causes, 

 e.g. heat and cold, may produce the same result, 

 this being caused, not by the special quality of 

 the abnormal factor, but by the fact of the passing 

 of the individual from a normal environment to 

 that which does not suit it. 



Among the exciting causes M. Pictet includes, 

 but apparently with some doubt, electricity and 

 mechanical vibration (trepidation) — the last, I 

 believe, has been abandoned. 



As regards the mechanism of variation, this has 

 its principal seat in the scales, all of which, 

 whether red, yellow, white, brown, or black, as 

 well as the blue and violet ones, are striated on 

 the surface so as to be capable of displaying the 

 optical colours, and most of which are more or 

 less filled with pigment in a granular form. The 

 optical effect is related to the quantity of pigment 

 in the scale, the intensity of the iridescence grow- 

 ing in inverse proportion to the pigment. In many 

 cases the basal part of a scale is less filled with 

 pigment than the distal part. Where the colours 

 of the wing are light, the scales generally contain 

 less pigment than where the colours are darker. 

 There are, however, white pigment scales, as in 

 the Pierids. 



There are various ways in which melanism may 

 be caused :■ — (i) The contained pigment may be 

 greater in quantity ; (2) it may be more strongly 

 oxidised, which darkens it; (3) where there are 

 both light and dark scales the latter may increase 

 in number ; (4) the scales may become so numerous 

 as to overlap each other, and thus reinforce the 

 darkness ; (5) the scales may be enlarged, which 

 increases the overlapping ; (6) dark hairs may 

 increase in number — like the scales, these are 

 susceptible of change in their colouring matter ; 

 (7) one face of the wing may appear darker if, 

 owing to the small quantity of pigment in its 

 scales, the darker opposite face of the wing shows. 

 Converse considerations apply to the causation 

 of albinism ; as regards (5), a very frequent 

 cause, the scales maj' so diminish in size that 

 instead of overlapping they scarcely touch, and 

 leave empty spaces ; they may diminish in size on 

 both sides of the wing, which thus becomes 

 transparent. (6) They may curl up at the sides, 

 producing similar consequences to those numbered 

 (4) and (5). 



There is a very interesting chapter on cases 

 where the optical and the pigmentary effects are 

 combined. Green in the Pierids is not caused by 

 green pigment, but by a mixture of yellow and 

 black scales having reflets bleus ; and in V. io the 

 violet and green is caused by red and yellow scales 

 mixed with white scales having reflets bleus. 



The cause of variation may be generally stated 

 thus. An individual which in the course of its 

 ontogeny makes less pigment than its congeners, 

 albinises; inversely, it melanises if it makes more 

 pigment than is normal ; the quantity of pigment 



