Page:The New International Encyclopædia 1st ed. v. 10.djvu/760

* INSTINCT. C72 INSTINCT. ard, from Murpliy's suggestion, infers that "in- !ccking is to select the adequate responses, and to steady the muscular mechanism to Its work. 'Automatic' responses are variable; the freshly hatched chicks at first in pecking make bad .shots us well as occasional good ones. KxAMPLE.s OF Ix.sTiNCTiVE AcT.s. In chicks: Pecking, walking, scratching themselves, preen- ing their down and leathers, stretching up and Happing their wings, scratching the earth, squat- ting down and dusting themselves, scattering and crouching when alarmed, making the danger churr and other sounds. In ducks: The way they seize and nunnble their food in the bill, their swimming, pijiing, smoothing the down of the breast with their bills, etc. Alligators on hatching rush with open jaws at anything presented to them, and bite it. In the higher animals, as birds and mammals, it is more dillicult to .separate instinctive from intelligent acts. The migrations of birds, and ix>rhaps of tlshcs, are variable, and Darwin says that this instinct "is occasionally lost." It should be observed that the migrations of birds, as of other animals, locusts, the reindeer. lemming, etc., are primarily reflex in their nature, being initiated by cold or the lack of food. Typical examples of the most striking and in- explicable instincts are the nesting habits of spiders, of the social insects, such as ants, wasps, and bees, those of birds, also of the muskrat and beaver, the mode practiced by worker bees ar- ranged in flics of ventilating by a peculiar move- ment of their wings, the well-closed hive, and the building of cells of the honeycomb by the hive-bee. Our present knowledge of the two chief groups of instincts may roughly and provisionally be classified thus: ( 1 ) Reflex acts mintfled with associative mem- en/ {consciousness or intelligence) : Mammals. Birds. Iteptiles. Amphibia (tree-frog). Fishes (certain bony fishes). Insects (especially the social species). Crustacea (certain lobsters and crabs). Spiders. Cephalopod mollusks. Snails (Helix). (2) Itcflcx ads only: Scorpion. King-crab. Sharks and floimders. .sridians. Molhisk.s. bivalves ( peleeypods ), and many univalves (gastropods). Echinodernis. Worms ( including annelids) . Cnelenterates, polyps, and actinians. Sponges. Protozoa (amceba>. monads, and infusorians) . The highest form of instincts are those of care for the young, or the eggs and nest, as shown by ants, certain fishes, and especially by birds and mammals. I'o.Mi'LKx iN.STixt'T.s. A complex instinct like that exhibited by the higher animals is generally regarded as the mingling of eon.seiousnes», or, as I..oel> and also Ucthe would call it, a.ssociative memory, with rellcii acts. The test is the ani- mal's capacity for learning or for being "trained to react in a desired way upon certain stinnili" or signs. It is seen in dogs, in the instincts of animals used in hunting, and in birds. In the lower vertebrates, memory is manifested. "Tree- frogs, for example, can be train<'d, upon hearing a sound, to go to a certain place for food," while other frogs, as the Kuro|N'an liana esciilcntu, ex- hibit no such capacity. Some fishes possess mem- ory, while its existence in sharks and in the flounder is doubtful. f-oeb protests against what he calls the an- thropomor|>hism of Romanes, Kimer, Prcyer, and others; l he <ipposcs the conclusions of IJethe, who denies that bees and ants possess associa- tive memory, though I.oeb himself thinks that they have little intelligence. The possibility of associative memory Loeb concedes in favor of spiders, certain '.-rustacea, and cephalopod mol- lusks. Complex instincts, often so mingled with in- cipient acts of intelligence as to astonish the observer, have repeatedly been noticed in the ants. They have the power of communicating with one another, and they are said to be sus- ce|)tible of education. ilore exact and critical views bearing on the origin of instincts have been expressed by Loeb, whose recent experiments and suggestions are noteworthy. Passing on to the subject of the greater com- plication of instinctive actions compared with those which are simple and reflex, "we have," he says, "to deal with a chain of reflexes in which the first relle.x becomes at the same time the cause which calls forth the second reflex." This is illustrated by the taking of food, of a lly, by the frog. Another example is the won- derful and hitherto inexplicable egg-laying habits of insects. Loeb explains that as meat-maggots are positively chemotropic (seeTROPiSM) toward decaying meat — i.e. are directed in their move- ments or "oriented by certain substances which radiate from a centre," just. as in the movements of hdiotropic animals toward the light — so the female flesh-fly "possesses the same positive chemotropism for these .substances as the larvte, and is accordingly led to the meat. As soon as the lly is seated on the meat, chemical stimuli seem to throw into activity the muscles of the sexual organs, and the eggs are deposited on the meat. It may also be possible that at the time when the fly is ready to deposit it.s eggs the posi- tive chemotropism is especially stnmgly devel- oped. It is only certain that neither ex|)erience nor volitifin plays any part in these processes." This explanation may also Ih? extended to all other insects, whether ovipositing on animal mat- ter or on the leaves of this or that plant, or, as in the case of ichneumon or other parasitic flies, upon or within the body of its accustomed host. Loeb recognizes the difficulty of analyzing the more complex instincts. The periodic depth mi- gration of marine pelagic animals is. he say«. a simple case of instinctive migrations, while