THE ACTION OF LIGHT, ETC. 



37; 



owls, though not decked out with any metallic 

 hues, differ little in the general character of their 

 coloration from their diurnal kindred, the hawks, 

 presenting bold, well-defined patterns, and a va- 

 riety of black, fawn, brown, buff, and white 

 shades. Few mammals display more vivid hues 

 than the Felidae, most of which are unquestiona- 

 bly nocturnal. Many nightly or subterranean in- 

 sects also, such as Spkodrus leucopthalmus and 

 Pri&tonychus (erricola, show T no signs of etiolation. 

 Even the common cockroach makes no approach 

 to that pallid, ghastly hue which is commonly 

 supposed characteristic of animals inhabiting 

 sunless localities. Among nocturnal species we 

 believe few, if any, instances can be found where 

 the male surpasses the female in brightness or 

 depth of coloring. 



Mr. Wallace, however, while going perhaps 

 even further than we should be prepared to ac- 

 company him in the rejection of the theory which 

 regards animal coloration as directly proportion- 

 ate to the intensity of solar radiation, gives some 

 curious instances of phenomena proving that in 

 certain cases light has a direct action upon the 

 colors of organic beings. Thus Mr. T. W. Wood, 

 some time ago, pointed out that the chrysalids 

 of the small "cabbage white" (Pontia rapce) va- 

 ried in color when the larvas had been fed up 

 in boxes lined with different colored materials. 

 Those which were kept in black boxes were nearly 

 black, while such as had lived in white boxes 

 were almost white. He observed corresponding 

 changes in the same species in a state of Nature : 

 chrysalids fixed against a whitewashed wall being 

 whitish ; those secured to a red-brick wall being 

 reddish ; while those fixed against a pitched pak 

 ing were nearly black. The cocoon of the em- 

 peror moth is also observed to be either white or 

 brown, in accordance with the colors of surround- 

 ing objects. A still more decisive instance of 

 such changes has been observed in the chrysalis 

 of Papilio Niretis, a South-African butterfly which 

 has been studied by Mrs. Barber. It acquires, 

 more or less exactly, the color of any contiguous 

 object. " A number of the caterpillars were 

 placed in a case with a glass cover, one side of the 

 case being formed by a red-brick wall, the other 

 sides being of yellowish wood. They were fed 

 on orange-leaves, and a branch of the bottle- 

 brush tree (Banksia) was also placed in the case. 

 When fully fed, some attached themselves to the 

 orange-twigs, others to the bottle-brush branch — 

 and these all changed to green pupae;. but each 

 corresponded exactly in tint to the leaves around 

 it, the one being a dark and the other a pale, 



faded green. Another attached itself to the wood, 

 and the pupa became of the same yellowish color ; 

 while one fixed itself just where the wood and 

 brick joined, and became one side red, the other 

 side yellow." 



This Mr. Wallace pronounces " a kind of nat- 

 ural photography, the particular colored rays to 

 which the fresh pupa is exposed in its soft, semi- 

 transparent condition effecting such a chemical 

 change in the organic juices as to produce the 

 same tint in the hardened skin." This power of 

 the pupa to assume the color of closely-adjacent 

 objects, however, is limited, since when Mrs. 

 Barber surrounded one of her caterpillars with a 

 piece of scarlet cloth the pupa displayed its ordi- 

 nary green tint, though the small red spots with 

 which it is marked were rendered abnormally 

 bright. It must be recorded, however, that these 

 very interesting changes are confined to the chrys- 

 alis, and do not appear to have extended in any 

 way to the mature butterfly. We have never 

 been able to trace any modification in the colors 

 of butterflies reared, for one generation, in ab- 

 normally colored light, nor, as far as we are 

 aware, has any other observer been more suc- 

 cessful. 



A correspondence has also been in some in- 

 stances traced between the colors of animals and 

 those of the localities which they inhabit and the 

 food which they eat. Spiders have been found 

 of exactly the same tint as the flowers in which 

 they lurk. Mr. Wallace, on the authority of Sir 

 Charles Dilke, mentions a pink-colored Mantis 

 which, when at rest, closely resembles the pink 

 flower of an orchis, and is thus enabled to seize 

 unsuspecting butterflies. But we should be wrong 

 in ascribing such similarity of coloration to the 

 effects of reflected light, or, indeed, of any merely 

 physical influence. They are almost certainly 

 due to physiological causes, and are instances of 

 what is called " protective coloration." 



There is another class of phenomena which at 

 first sight seems due to the action of light. Many 

 insects when they first emerge from the pupa are 

 abnormally pale, and do not take their full ma- 

 ture coloration until after a longer or shorter in- 

 terval of time. It was in virtue of this property 

 that an entomologist, commissioned by the Ger- 

 man Government to inspect a field where the 

 dreaded Colorado beetle had made its appear- 

 ance, was enabled to decide that these insect en- 

 emies had only just appeared in the mature form, 

 and that on turning up the ground a further stock 

 would be found in a rudimentary state, as on 

 actual trial was found to be the case. But this 



