COLOR IN ANIMALS. 471 



the metallic coloring ; while plants and zoophytes are without reflect- 

 insc shades. The moUusca take a middle path with their hue of mother- 

 of-pearl. What is the reason of these arrangements in the animal king- 

 dom ? It is a question which cannot be satisfactorily answered ; but 

 some observations have been made which throw light on the subject. 

 One is, that among animals, the part of the body turned toward the 

 earth is always paler than that w^hich is uppermost. The action of 

 light is here apj)arent. Fishes which live on the side, as the sole and 

 turbot, have the left side, which answers to the back, of a dark tint; 

 while the other side is white. It may be noticed that birds which fly, 

 as it were, bathed in light, do not ofler the strong contrast of tone be- 

 tween the upper and lower side. Beetles, wasj^s, and flies, have the 

 metallic coloring of blue and green, possess rings equally dark all 

 round the body; and the wings of many butterflies are as beautifully 

 feathered below as above. 



On the other hand, mollusca which live in an almost closed shell, 

 like the oyster, are nearly colorless ; the larvie of insects found in the 

 ground or in wood have the same whiteness, as well as all intestinal 

 worms shut up in obscurity. Some insects whose life is spent in dark- 

 ness keep this appearance all their lives ; such as the curious little 

 beetles inhabiting the inaccessible crevasses of snowy mountains, in 

 whose depths they are hidden. They seem to fly from light as from 

 death, and are only found at certain seasons, wdien they crawl on the 

 flooring of the caves like larvie, without eyes, which would be useless 

 in the retreats where they usually dwell. 



This relation between coloring and light is very evident in the be- 

 ings wdiich inhabit the earth and the air ; those are the most brill- 

 iant which are exposed to the sun ; those of the tropics are brighter 

 than in the regions around the north - pole, and the diurnal species 

 than the nocturnal ; but the same law does not apparently belong to 

 the inhabitants of the sea, which are of a richer shade where the light 

 is more tempered. The most dazzling corals are those which hang 

 under the natural cornices of the rocks and on the sides of submarine 

 grottoes ; while some kinds of fish, which are found on the shores as well 

 as in depths requiring the drag-net, have a bright-red purple in the lat- 

 ter regions, and an insignificant yellow brown in the former. Those 

 who bring up gold-fish know well that, to have them finely colored, 

 they must place them in a shaded vase, where aquatic plants hide them 

 from the extreme solar heat. Under a hot July sun they lose their 

 beauty. 



The causes to which animal coloring is due are very various. Some 

 living substances have it in themselves, owing to molecular arrange- 

 ment, but usually this is not the case ; the liveliest colors are not bound 

 up with the tissues. Sometimes they arise from a phenomenon like 

 that by which the soap-bubble shows its prismatic hues ; sometimes 

 there is a special matter called pigment which is united with the or- 



