COLOR IN ANIMALS. 473 



stem, offers a series of small squares of horny substance placed point 

 to point. These plates, of infinitesimal size, are extremely thin, brown, 

 and, to all appearance, exactly alike, whatever may be the reflection 

 they give. The brilliant large feathers of the peacock are the same ; 

 the plates are only at a greater distance, and of less brightness. They 

 have been described as so many little mirrors, but that comparison is 

 not correct, for then they would only give back light without color- 

 ing it. Neither do they act by decomposing the rays which pass 

 through them, for then they would not lose their iris tints under the 

 microscope. It is to metals alone that the metallic plumage of the 

 humming-birds can be compared ; the effects of the plates in a feather 

 are like tempered steel or crystallized bismuth. Certain specimens 

 emit colors very variable under different angles, the same scarlet 

 feather becoming, when turned to ninety degrees, a beautiful emerald 

 green. 



The same process which Nature has followed in the hummino--bird 

 is also found in the wing of the butterfly. It is covered with microscopic 

 scales, which play the part of the feather, arranged like the tiles of a 

 house, and taking the most elegant forms. They also lose their color 

 under magnifying power, and the quality of reflection shows that the 

 phenomena are the same as in feathers. There is, however, a differ- 

 ence in the extent of the chromatic scale. While the humming-bird 

 partakes in its colors of the whole of the spectrum from the violet to 

 the red, passing through green, those of the butterfly prefer the more 

 refrangible ones from green to violet, passing through blue. The ad- 

 mirable lilac shade of the Morpho menelas and the Morpho cypris is 

 well known, and the wings of these butterflies have been used by the 

 jewelers, carefully laid under a thin plate of mica, and made into or- 

 naments. A bright green is not uncommon, but the metallic red is 

 rare, excepting in a beautiful butterfly of Madagascar, closely allied 

 to one found in India and Ceylon. The latter has wings of a velvet 

 black with brilliant green spots ; in the former, these give place to a 

 mark of fiery red. 



There is the same difference between the metallic hues of creatures 

 endowed with flight and the iris shades of fishes, that there is between 

 crystallized bismuth and the soft reflections of the changing opal. To 

 have an idea of the richness of the fish, it is only necessary to see 

 a net landed filled with shad or other bright fish. It is one immense 

 opal, with the same transparency of shade seen through the scales, 

 which afford the only means of imitating pearls. It is due, however, 

 not to the scales, but to extremely thin layers lying below the scales 

 under the skin and round the blood-vessels, w^hich look like so many 

 threads of silver running through the flesh. Reaumur first noticed 

 and described them ; sometimes their form is as regular as that of a 

 crystal, and of infinitesimal size and thickness. The art of the mak- 

 ers of false pearls is to collect these plates in a mass from the fish, and 



