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1、Passage Thirteen (Cryptic Coloring)Cryptic coloring is by far the commonest use of color in the struggle for existence.It is employed for the purpose of attack (aggressive resemblance or anticryptic coloring ) as well as of defense (protective resemblance or procryptic coloring ).The fact that the s
2、ame method concealment, may be used both for attack and defense has been well explained by T.Belt who suggests as an illustration the rapidity of movement which is also made use of by both pursuer and pursued, which is similarly raised to a maximum in both by the gradual dying out of the slowest thr
3、ough a series of generations.Cryptic coloring is commonly associated with other aids in the struggle for life.Thus well-concealed mammals and birds, when discovered, will generally endeavor to escape by speed and will often attempt to defend themselves actively.On the other hand, small animals which
4、 have no means of active defense, such as large, numbers of insects, frequently depend upon concealment alone.Protective resemblance is far commoner among animals than aggressive resemblance, in correspondence with the fact that predaceous forms are as a rule much larger and much less numerous than
5、their prey.In the case of insectivorous Vertebrata and their prey such differences exist in an exaggerated form.Cryptic coloring, whether used for defense of attack, may be either general or special.In general resemblance the animal, in consequence of its coloring, produces the same effect as its en
6、vironment, but the conditions do not require any special adaptation of shape and outline.General resemblance is especially common among the animal inhabiting some uniformly colored expanse of the earths surface, such as an ocean or a desert.In the former, animals of all shapes are frequently protect
7、ed by their transparent blue color, on the latter, equally diverse forms are defended by their sandy appearance.The effect of a uniform appearance may be produced by a combination of tints in startling contrast.Thus the black and white stripes of the zebra blend together at a little distance, and “t
8、heir proportion is such as exactly to match the pale tint which arid ground possesses when seen by moonlight.” Special resemblance is far commoner than general and is the form which is usually met with on the diversified surface of the earth, on the shores, and in shallow water, as well as on the fl
9、oating masses of algae on the surface of the ocean, such as the Sargasso Sea.In these environments the cryptic coloring of animals is usually aided by special modifications of shape, and by the instinct which leads them to assume particular attitudes.Complete stillness and the assumption of a certai
10、n attitude play an essential part in general resemblance on land; but in special resemblance the attitude is often highly specialized, and perhaps more important than any other element in the complex method by which concealment is effected.In special resemblance the combination of coloring, shape, a
11、nd attitude is such as to produce a more or less exact resemblance to some one of the objects in the environment, such as a leaf of twig, a patch of lichen, a flake of bark.In all cases the resemblance is to some object which is of no interest to the enemy or prey respectively.The animal is not hidd
12、en from view by becoming indistinguishable from its background as in the case of general resemblance, but it is mistaken for some well-know object.In seeking the interpretation of these most interesting and elaborate adaptations, attempts have been made along two lines.The first seeks to explain the
13、 effect as a result of the direct influence of the environment upon the individual (G.L.L.Buffon), or by the inherited effects of efforts and the use and disuse of parts (J.B.P.Lamarck).The second believes that natural selection produced the result and afterwards maintained it by the survival of the
14、 best concealed in each generation.The former suggestion breaks down when the complex nature of numerous special resemblances is appreciated.Thus the arrangement of colors of many kinds into an appropriate pattern requires the cooperation of a suitable shape and the rigidly exact adoption of a certa
15、in elaborate attitude.The latter is instinctive and thus depends on the central nervous system.The cryptic effect is due to the exact cooperation of all these factors; and in the present state of science, the only possible hole of an interpretation lies in the theory of natural selection, which can
16、accumulate any and every variation which tends toward survival.A few of the chief types of methods by which concealment is effected may be briefly described.The colors of large numbers of vertebrate animals are darkest on the back and become gradually lighter on the sides, passing into white on the belly.Abbot H.Thayer has suggested that this gradation obliterates the appearance of solidity, which is due to shadow.The color harmony, which is also essential to concealment, is produced beca
