National Geographic : 1927 Jan
LIFE ON A CORAL REEF also fit perfectly into depressions in the smooth surface countersunk to receive them. The hand might be passed back over them without the sense of touch dis covering them, so precise is the work manship. In the matter of color, similar perfec tion in detail is manifest. When the pec toral fin is fully extended it stands hori zontally out at right angles to the body. The ventrals similarly extended are spread in the same horizontal plane, and the upper surfaces of all are dark like the back; but the lower surface of the extended pectoral is glistening silver, and that of the ventral fin pure lusterless white. As a result, when they are appressed to the body they not only sink into the depressions waiting to receive them, but the one pair is lost in the metallic silver of the side and the other in the flat white of the belly, with which they agree pre cisely in their respective positions. By contrast, had I not had the good fortune to see them using their odd equip ment, I should never have known why a large mantis shrimp at Tortugas has the last joint of its walking legs studded with bristles until they look like bottle brushes, or why the little crab Petrolisthes has on each joint of its last limbs, serving as jaws, a great tuft of fringed hairs. I flexed and extended the maxillipeds of Petrolisthes, spread out the hair tufts that readily opened; yet the essence of their function escaped me before, in a fissure facing the tide, I saw the creatures throw these organs wide to form a great hemispherical funnel that caught drift ing microscopic material until inturned, cleaned, and held forth again for Nature's bounty. And I venture to say regarding the shrimp that no mere anatomical study, however thorough, would ever induce in the mind's eye a clear image of the ani mal standing in its burrow in incoherent sand, with its several pairs of flattened palms, its crooked elbows, and ten bushy feet bearing against the walls and keep ing them from collapsing. FIELD STUDY ALONE CAN SOLVE MANY RIDDLES Here the difficulty in conceiving the service rendered by elaborate structures is due solely to that in visualizing the con ditions under which they function, though these themselves, when discovered, may prove rather simple. But where the element of compromise, to which I have referred earlier (see text, page 81), enters as it frequently does in the realm of coloration, field study-and then more field study-is absolutely neces sary before the often marvelously effective disguises may be apprehended in their true relations. On a ground color that matches one background against which it is commonly seen, bars appear, matching another en tirely different. Contrastive patterns in gay colors result, which seem impossible to explain as useful; but to the enlight ened eye these, no less than the more ob viously serviceable structures described, illustrate that adaptation to environment which characterizes not only animals of the coral reefs, but which from the time of Aristotle has been recognized as a dis tinctive feature of living things. Notice of change of address of your NATIONAL GEOGRAPHIC MAGAZINE should be received in the office of the National Geographic Society by the first of the month to affect the following month's issue. For instance, if you desire the address changed for your March number, the Society should be notified of your new address not later than February first.