Page:The New International Encyclopædia 1st ed. v. 16.djvu/534

* PROTECTIVE COLORATION. 466 PROTECTIVE COLORATION. The blandiing of the hairs is due to partial, not entire, depigmentation. Color Pbeierence. Different aquatic animals exhibit a marked preference for certain colors of the spectrum in which they 'feel better.' The little fresh-water crustacean Daphnia prefers to swim in orange, yellow, and especially gi eeu rays. The starfish shuns the red rays. Animals which love the light, as bees, prefer blue or green rays, wliile the light-shuiuiing or lucifugous insects, such as ants, have less antipathy for red than for other colors. In such cases it has been thought by Cufnot that light doubtless acts as an e.xcitant oh respiration. As has been repeatedly noticed, the common liouse-fly prefers green to lavender, and black to white. On the other hand, locusts are attracted and will alight upon white or light- colored clothes, and not be attracted by dark. The preference of Hies for dark clotli may be due to the fact that it absorbs more heat than white cloth, and thus favors quicker respiration and greater activity, especially in the coolness of the autunni. Protection Due to Conspicuous Bars, Stripes, and Spots, Although the giraffe, the zebra, and the jaguar seem most consjiicuously colored, we are assured that the spots upon the jaguar, for example, harmonize with the oval patches of sunlight. Sir Samuel Baker says that the striped skin of the tiger harmonizes with dry sticks, yellowish tufts of grass, and the re- mains of burnt stumps of its liabitat, and even the giraffe is far from conspicuous when foimd in its native forests. The African antelopes are strikingly marked on the. body and head as well as the feet with white stripes and patches in general like those of zebras, which Pocock re- gards as "representing spots or streaks of sun- light passing through foliage or reflected from leaves," and that these marks are for protection rather than for recognition. He thinks that such markings come within the scope of Thayer's hy- pothesis of concealment by the counteraction of light and shade. Of the species of elands of Africa one lives in the forest and is reddisli and conspicuously striped with white, the neck being black : on the other hand, the common eland is dun-colored with no sign of stripes and lives in deserts. So it is with the koodoos ; the lesser one living in thick jungles is much more strikingly marked than the larger species which lives in liilly mountainous regions or on the open plains. JIiMiCRY. :Iany butterflies of the group Heli- conidiie are associated with species of Leptalis belonging to another family (Pierida-) which copy the heliconid butterflies in form and color, and which, probably owing to a bad odor secreted by glan<ls in the end of the body, are distasteful to birds. It is supposed by Bates, Wallace, Dar- win, and others that were not the mimics dis- guised as heliconias they would be devoured by birds and tlius become extinct. These authors believe that the resemblance has been brought about by natural selection. In his "Contributions to an Insect Fauna of the Amazon Valley," Henry Walter Bates (q.v.) calls attention to the fact that a large number of the species of Heliconida; "are accompanied in the districts they inhabit by other species which counterfeit them." Ac- cording to Fritz Miiller (although Bates states the same idea ). the species serving as the model, being unpalatable to birds on account of its re- pulsive taste and odor, is therefore safe from its foes, while the mimic, which has no bad taste or odor, is protected from attack. Mr. Bates's own views are moderate compared with those of Wal- lace and later extreme advocates of Darwinian mimicry. In his original essay Bates sliowa that the majority of the species of Heli- conidiE have very limited ranges, and con- tends that the cause of the formation of the local varieties is "the direct action of phys- ical conditions on the individuals." Several entomologists, Ehves, Packard and others, have not accepted the hypothesis of Bates and Miiller, that the mimicry is due to natural selection, but hold that the niimicrj' is accidental and due to convergence to similarities in the environment. The markings, such as similar hues in models and mimics, bars and spots, Packard believes are due to such effects of light and sliade. moist- ure and temperature, as liave produced them in birds, mammals, and reptiles. They may be perpet- uated and preserved by natural selection, but the primary cause of this originally is the action of the physical agents mentioned, or at least environ- mental causes afl'ecting both models and mimics, iluch stress is laid on the attacks of birds in bring- ing about or aiding the process of natural selection of these markings. It is. however, to be observed that neither Bates, Miiller. nor Wallace, all of wliom lived for many years in the tropics, has ever seen a bird chase and devour butterflies. In fact, only a few insectivorous birds catch butter- flies or care to chase them. After several years' special research on the habits of sparrows and other insectivorous birds, Judd states in a report to the United States Department of Agriculture that he does not know of any kind of bird "that feeds upon butterflies during any month of the year to the extent of one-tenth of one per cent, of its food." It thus appears from a comprehensive survey of the markings of animals of difl'erent classes, living both in the sea and on land, that the causes of the similarity in their markings are due to the effects of light and shade, also perhaps to moist- ure — at all events to the action of the surround- ings. It should also be borne in mind that the range of primary colors is not ver' great, nor of stripes and bars; under similar physical condi- tions the colors and spots and stripes and their location on the body are repeated in animals of difl'erent groups and species. Nature is limited in the disposal of ornamental features. Hence models and mimics may be protectively orna- mented with the same hues and patterns, and it is probable that selection and the attacks of birds and lizards have had little to do with the origination of protective coloration. BiBLioGKAPiiY. Darwin, Origin of Species (London, 1S59), Dcscch* of Mayi (ib. 1874) ; Wal- lace, Darwinisms (New York, 1889) ; Bates, "Con- tributions to an Insect Fauna of the Amazon Valley. Lepidoptera: Heliconida?," Transactions Linncan Society of London, vol. xxiii. (18(V2); Packard, Half Hours With Insects (Boston, 1S77) ; Scudder, liiitterflies of the Eastern United States (ib., 1887-89) : iliiller. Transactions of the Entomological Society (London, 1870) ; Poul- ton. The Colors of Animals (New York, 1890) ; Beddard, Animal Coloration (ib„ 1S95) ; Belt, The Naturalist in Sicarar/ua (London, 1874) ; Morgan, Animal Life and Intelligence (ib.. 1890- 91): Eimer, Organic Erolution (ib., 1890); Marshall and Poulton, "Bionomics of South