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The rugged outline of a mountain peak looks like a human face; the markings on a moth show a skull and crossbones. Mere coincidences we say, and dismiss the matter as another freak of nature. But when we come across an animal that looks like a leaf or a twig, we begin to wonder. This likeness must be more than chance--it must play an important part in the animal's survival. This brings us straight to the crux of our problem: the function of outward appearances.
We have all seen insects that are the color of bark and brooding pheasant hens whose feathers seem like the fleeting shadows of their nesting ground. We may have chanced upon a moth whose only protection is the coloring that makes it resemble a wasp. Each of these animals pretends to be something it is not, and it does this in order to survive. Modern armies use camouflage to protect their soldiers, guns, ships, and military installations; the result is proof positive of the defensive value of such techniques. The reader will not be surprised then, if we tell him that our subject has played a prominent part in all discussions about the origin and the evolution of living organisms. Charles Darwin was one of the first to stress the importance of camouflage, and since his day the subject has formed one of the strands of biological theory.
This is not to say that the authorities all agree. What some choose to explain as camouflage, others describe in altogether different terms. A host of experimenters has set out to prove the various theories, but always with perfect scientific detachment. The problem of mimicry, in particular, has become a veritable no man's land of biological battle.
These are things our book will explore. Casting our glance over a vast canvas, we shall try to trace the
meaning of some of the colorful brush strokes that went into its painting.
the year, even in the deepest snow. The blue strain is dominant, and it persists even when the animals are cross-bred. Such foxes are less fertile, but even so the blue strain accounts for roughly 50 per cent of the total fox population of certain regions of East Greenland. Rapid Color Changes The quick color changes of fishes, amphibians, lizards, cuttlefish, squids, shrimps, and other crustaceans are due to special cells, the chromatophores, which work either independently or in an organization
Media America, Inc. www.questia.com Publication Information: Book Title: Animal Camouflage. Contributors: Adolf Portmann - author. Publisher: University of Michigan Press. Place of Publication: Ann Arbor, MI. Publication Year: 1959. Page Number: 15. 13 title FIG. 10. As the nightjar broods on the ground, it feels safe enough to yawn while being photographed. (Photograph: E. Hosking.) Figure 11 shows how disguise can be combined with conspicuous markings for use on special occasions. During
MI. Publication Year: 1959. Page Number: 17. 15 title from an animal or else to be attracted by it. Many butterflies have independent patterns on forewings and hindwings; this is conspicuous in butterfly collections in which the wings are unnaturally extended. Yet, in real life, the wings produce a quite deceptive symmetrical pattern ( Fig. 13 ). This symmetry poses important genetic problems which we shall examine more closely. The Joining Effect In the development of the embryo the original
its own masking method: thus Maia verrucosa always starts with the head and often leaves it at that, and Posidonia lengthens the head--and thus the whole body--by applying strips of material, while Inachus scorpio only camouflages its first pair of FIG. 39. The pincers of a masked crab (Hyas) are extremely agile and can reach every part of the body that is covered with bristles. (After Aurivillius.) -36Questia Media America, Inc. www.questia.com Publication Information: Book Title: Animal
of Publication: Ann Arbor, MI. Publication Year: 1959. Page Number: 40. 38 title FIG. 45 Left: a carrier snail (Xenophora) with shells; right: a snail (Xenophora solaris) with calcium spikes and with shells added during earlier stages. (Photograph: H. R. Haefelfinger.) camouflage is but one of a wide range of different functions in one and the same field. In mollusks this field stretches from marginal spikes to the selection of foreign matter--from pure ornamentation to complete disguise. 4.