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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



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, sp.) 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 dark, the other 

 a pale, faded green. Another attached itself to 

 the wood, and the pupa became of the same yel- 

 lowish color; while one fixed itself just where 

 the wood and brick joined, and became one side 

 red, the other side yellow ! These remarkable 

 changes would perhaps not have been credited, 

 had it not been for the previous observations of 

 Mr. Wood ; but the two support each other, and 

 oblige us to accept them as actual phenomena. 

 It is a kind of natural photography, the particu- 

 lar 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. It 

 is interesting, however, to note that the range of 

 color that can be acquired seems to be limited to 

 those of natural objects to which the pupa is 

 likely to be attached ; for when Mrs. Barber sur- 

 rounded one of the caterpillars with a piece of 

 scarlet cloth no change of color at all was pro- 

 duced, the pupa being of the usual green tint, 

 but the small red spots with which it is marked 

 were brighter than usual. 



In these caterpillars and pupae, as well as in 

 the great majority of cases in which a change of 

 color occurs in animals, the action is quite in- 

 voluntary ; but among some of the higher animals 

 the color of the integument can be modified at 

 the will of the animal, or, at all events, by a re- 

 flex action dependent on sensation. The most 

 remarkable case of this kind occurs with the 

 chameleon, which has the power of changing its 

 color from dull white to a variety of tints. This 

 singular power has been traced to two layers of 

 pigment deeply seated in the skin, from which 

 minute tubes, or capillary vessels, rise to the sur- 

 face. The pigment-layers are bluish and yellow- 

 ish, and by the pressure of suitable muscles these 

 can be forced upward either together or separate- 

 ly. When no pressure is exerted the color is dirty 

 white, which changes to various tints of bluish, 

 green, yellow, or brown, as more or less of either 

 pigment is forced up and rendered visible. The 

 animal is excessively sluggish and defenseless, and 

 its power of changing its color to harmonize with 

 surrounding objects is essential to its existence. 



Here, too, as with the pupa of Papilio Nireus, 

 colors such as scarlet or blue, which do not occur 

 in the immediate environment of the animal, can- 

 not be produced. Somewhat similar changes of 

 color occur in some prawns and flat-fish, accord- 

 ing to the color of the bottom on which they 

 rest. This is very striking in the chameleon- 

 shrimp {Mysis Chamceleon), which is gray when 

 on sand, but brown or green when among sea- 

 weed of these two colors. Experiment shows, 

 however, that when blinded the change does not 

 occur, so that here too we probably have a vol- 

 untary or reflex sense-action. Many cases are 

 known among insects in which the same species 

 has a different tint according to its surroundings, 

 this being particularly marked in some South 

 African locusts which correspond with the color 

 of the soil wherever they are found ; while sev- 

 eral caterpillars which feed on two or more 

 plants vary in color accordingly. Several such 

 changes are quoted by Mr. R. Meldola, in a paper 

 on " Variable Protective Coloring in Insects " 

 (" Proceedings of the Zoological Society of Lon- 

 don," 1873, page 153), and some of them may 

 perhaps be due to a photographic action of the 

 reflected light. In other cases, however, it has 

 been shown that green chlorophyll remains un- 

 changed in the tissues of leaf-eating insects, and 

 being discernible through the transparent integ- 

 ument produces the same color as that of the 

 food-plant. 



These peculiar powers of change of color and 

 adaptation are, however, rare and quite excep- 

 tional. As a rule there is no direct connection 

 between the colors of organisms and the kind of 

 light to which they are usually exposed. This is 

 well seen in most fishes, and in such marine ani- 

 mals as porpoises, whose backs are always dark, 

 although this part is exposed to the blue and 

 white light of the sky and clouds, while their 

 bellies are very generally white, although these 

 are constantly subjected to the deep-blue or 

 dusky-green light from the bottom. It is evi- 

 dent, however, that these two tints have been 

 acquired for concealment and protection. Look- 

 ing down on the dark back of a fish it is almost 

 invisible, while to an enemy looking up from 

 below the light under-surface would be equally 

 invisible against the light of the clouds and sky. 

 Again, the gorgeous colors of the butterflies 

 which inhabit the depths of tropical forests bear 

 no relation to the kind of light that falls upon 

 them, coming as it does almost wholly from 

 green foliage, dark -brown soil or blue sky; and 

 the bright under-wings of many moths which are 



