March 17, 1887] 



NATURE 



471 



(y) The General Surface of the Skin.—'X\\\% was tested 

 by conjlicting colour expert men/ s. It had been previously 

 shown that the larvK were sensitive during stage iii., and 

 therefore they were covered in this stage with conipart- 

 mentcd tubes, so constructed that the head and anterior 

 part of the body hung in the lower chamber of one colour, 

 while the posterior part of the body was in the upper 

 chamber in another colour. In another method the larvae 

 were hung upon a vertical surface, while the head and 

 front part of the body passed through a hole in a shelf, 

 the vertical surface above the shelf, and the upper side of 

 the shelf itself being one colour, while the vertical surface 

 below the shelf and the lower side of the shelf were of the 

 colour tending to produce the most opposite effects. The 

 result of all these experiments was to show that the colour 

 influence does act on some element of the larval skin, and 

 that the larger the area of skin exposed to any one colour 

 the moredoes the pupa follow its inlluence. Parti coloured 

 pupa; were not obtained, thus perhaps pointing towards 

 the action of the nervous system rather than towards the 

 direct action of light on or through the skin itself. 



6. The Xti/ure of the Effec/s Produced. — The colouring- 

 matter of the dark pupffi is contained in a thin super- 

 ficial layer of the cuticle ; below this is a thicker layer 

 divided into exceedingly delicate lamella, between which 

 fluids are present, and the latter form the thin plates 

 which, by causing interference of light, produce the 

 brilliant metallic appearance. The thinner upper layer, 

 being dark, acts as a screen in the dark pupx. Precisely 

 the same metallic appearances are caused by the films of 

 air between the thin plates of glass which are formed on 

 the surface of bottles long exposed to earth and moisture. 

 Both have the same spectroscopic characters and the 

 same transmitted colours (complementary to those seen 

 by reflection). The brilliancy of the cuticle can be pre- 

 served in spirit for any length of time; it disappears on 

 drying, but can be renewed on wetting (this had been 

 previously known), and the colours are seen to change 

 during the process of drying, and when the cuticle is 

 pressed, for the films are thus made thinner. The same 

 lamellated layer exists in non-metallic pupa: of other 

 species, and is used as a reflector for transparent colouring- 

 matter contained in its outer lamella;. Thus the structure 

 which rendered possible the brilliant effects due to inter- 

 ference probably existed long before these special eftects 

 were obtained, and was used for a different purpose. 



7. The niolo^^^ical Value of the Gilded Appearance.— 

 It is probable that the gilded pupae of Vanessidas re- 

 semble glittering minerals such as mica (which is ver>- 

 common in many places) ; their shape is very angular, 

 and like that of minerals : conversely the gray pups 

 resemble gray and weathered rock-surfaces, and the two 

 conditions of rock would themselves act as a stimulus for 

 the production of pupa; of corresponding colour. The 

 power was probably gained in some dry hot country, 

 where mineral surfaces do not weather quickly Once 

 formed, it may be used for other purposes, and in certain 

 species is probably a warning to the enemies that the 

 insect is inedible. It is interesting to note how the 

 Vanessida;, primarily coloured so as to resemble mineral 

 surroundings, are modified for pupation on plants. Thus 

 Vaiussa lo has a green form which is produced among 

 leaves ; V. ntalanla has no green form, and spins to- 

 gether the leaves for concealment, but both these species 

 commonly pupate freely exposed on mineral surfaces ; 

 V. uriide has neither the green form nor the habit of 

 concealment, and it has a strong disinclination to pupate 

 on its food-plant, as many observations concurred in 

 proving. 



III. Experiments upon Vanessa atalanta. — This spe- 

 cies was also made brilliantly golden or dark-coloured 

 by the use of appropriate surroundings in the larval 

 condition. 



IV. E.xperimenls upon Papilio machaon. — This species. 



\\V.^ P. polydamus (Fritz Miiller), has no power of being 

 influenced by surrounding colours. A brown pupa was 

 obtained on the food-plant, and many green ones upon 

 brown twigs, &c. It is possible that the amount of shade 

 may determine the formation of the dark pupa irrespective 

 of colour, or that less healthy and smaller larvae may 

 produce the brown form, just as diseased Vanessa larvae 

 produce gilded pupae. 



V. Experiments upon Pieris brassicce and P. rapcB. 



1. Effeds of Colours. — Black produced dark pups, and 

 the greater the illumination the darker the pupse {P. 

 rapte), this result being the reverse of that obtained with 

 V. urticce ; white produced light pupae, and the greater 

 the illumination the lighter the pups {P. rapes) ; dark 

 red (P. brassicce) produced dark pups ; deep orange, in 

 both species, produced very light pups of a green colour ; 

 pale ycllozii and yelloii'ish green produced rather darker 

 pups than the orange ; I'luish-green produced much 

 darker pups ; while dark blue produced still d.arker pupae 

 {P. rapie only). Hence there is a remarkable and sudden 

 fall, followed by a slow and gradual rise in the amount 

 of pigment formed as the light from various parts of the 

 spectrum from red to blue predominates in the reflected 

 rays which fall on the larval surface. But their effects on 

 the formation of superficially placed dark pigment are 

 accompanied by changes affecting the formation of 

 greens and yellows, &c., in the deeper sub-cuticular 

 tissues. Hence the results of any given stimulus are 

 exceedingly complicated. 



2. Other Experiments. — It was shown by the method 

 described above that the ocelli are not sensitive in this 

 species, and by similar transference experiments it was 

 proved that the influence acts on the larva and not on 

 the pupa itself. 



VI. Experiments upon Ephyra pendularia. — In this 

 genus of moths the exposed pups are often green and 

 brown in different individuals, but these colours follow 

 the corresponding tints of the larvs, and therefore cannot 

 be influenced unless the latter themselves were changed, 

 and such susceptibility in the larval state has not been 

 proved for this genus. This is the only known instance 

 of a constant relation between the larval and pupal 

 colours. 



VII. Experiments upon the Cocoon of Saturnia carpini. 

 ■ — It was found that the larvs spin dark cocoons in black 

 surroundings, but white ones in lighter surroundings. 



NOTES 



The principal officers for the Manchester meeting of the 

 British Association, to begin on August 31, under the presidency 

 of Sir Henry Roscoe, have now been selected. The following 

 will be the Presidents of the various Sections : — Section .\, 

 Mathematics and Physics, Sir Robert S. Ball, Astronomer 

 Royal for Ireland ; B, Chemistry, Dr. Edward Schunck, F. R.S. ; 

 C, Geology, Dr. Henry Woodward, F. R. S. ; D, Biology, Prof. 

 A. Newton, F.R.S. ; E, Geography, General Sir Charies 

 Warren, R.E., G.C.M.G. ; F, Economic Science, Dr. Robert 

 Giffen ; G, Mechanical Science, Prof. Osborne Reynolds, 

 F.R.S. For Section H, Anthropology, a President has not yet 

 been chosen. One of the public lectures will be given by 

 Prof. H. B. Dixon, who has taken as his subject " The Rate of 

 Explosions in Gases." The lecture to the working classes will 

 be given by Prof. George Forbes. It is expected that, socially, 

 the Manchester meeting will be one of the most brilliant ever 

 held. A very large sum has already been subscribed, and liberal 

 arrangements are being made for excursions and other enter- 

 tainments. 



The trustees of the fund established by Mrs. Elizabeth 

 Thompson, of Stamford, Connecticut, "for the advance- 

 ment and prosecution of scientific research in its broadest 



