Page images
PDF
EPUB

REFLEX AND INSTINCTIVE ACTIONS.

525

of power to use them aright), is to study the particular defect under which the individual suffers; and then to make him practise systematically the various movements concerned in the production of the sounds in question, at first separately, and afterwards in combination, until he feels that his voluntary control over them is complete.

CHAPTER XIV.

OF INSTINCT AND INTELLIGENCE.

692. It will be remembered that, when the Nervous System was described (Chap. XI.), it was shown to be the instrument of three classes of operations, each of which seems to be performed by a distinct portion of the apparatus.-I. The first of these is the class of simply Reflex actions, which are executed only in respondence or answer to impressions made upon the nerves proceeding to a ganglionic centre; as when a Dytiscus, whose head has been cut off, executes swimming movements immediately that its feet come in contact with water. These movements evidently take place without any choice or direction on the part of the animal, which, in executing them, seems like a mere machine adapted to perform certain actions when certain springs are touched; and it has been shown that they may be called-forth even without its consciousness. Of these reflex movements, the Spinal Cord of Vertebrata, and in Invertebrata the ganglia corresponding to it (in regard to their connexions with the organs of locomotion, respiration, &c.), are the instruments.-II. The second class comprehends those Instinctive actions, which differ from the preceding in being dependent on the sensations received by the animal, and in being, therefore, never performed without its consciousNevertheless, the animal in executing them is not guided by any perception of the object to be attained, or by any choice of the means by which it is to be accomplished; but acts blindly and involuntarily, in accordance with an irresistible impulse, implanted in it by its Creator for the purpose of causing it to do that, without or even against its Will, which it would not have chosen or devised by its very imperfect intelligence. The actions of this class are most

ness.

526 RELATION OF INSTINCTIVE TO INTELLIGENTIAL ACTIONS.

wonderful in the Invertebrata, which possess the least Intelligence; and, on the contrary, they are fewest and least remarkable in Man, whose Intelligence is highest. From the constant proportion they bear to the size of the ganglia of sensation, which form nearly the whole nervous mass in the head of Insects, &c., and a large part of that of the lower Vertebrata, but which are comparatively small in the Mammalia and especially so in Man, there seems good reason to regard these organs as their chief instruments.-III. The third and highest class of actions, is that in which Intelligence is the guide, and the Will the immediate agent. The animal receives sensations, forms a notion of their cause, reasons upon the ideas thus excited, perceives the end to be attained, chooses or devises the means of accomplishing it, and voluntarily puts those means into execution. These actions are seen, in their highest and most complete form, in Man; but they are not confined to him; for, as will be shown hereafter, true reasoning processes are performed by many of the lower animals. There can be no doubt that the Cerebral Hemispheres, which form the Brain properly so called, constitute the instrument by which these actions are executed; for we find that their size and development bear a very regular proportion to the degree of Intelligence which the animal

possesses.

693. It follows, then, that the lower we descend in the scale of Animal life, the larger is the proportion of the movements of any particular species which we are to attribute to the Reflex and the Instinctive classes; whilst the proportion which is due to Intelligence and Will diminishes in a like degree. Thus we have seen that the ordinary movements of locomotion, which Man performs in the first instance by voluntary effort, are reflex in Insects (§ 445); and there can be no reasonable doubt that the movements of the tentacula of the Hydra, by which it entraps its prey and draws it to the entrance of its stomach (§ 121), are of a reflex, rather than a voluntary or instinctive character, since they are obviously analogous to those movements of the pharyngeal muscles, by which the food is grasped and carried into the alimentary tube of the highest animals (§ 195). There is one curious fact, which would seem to indicate a difference between them, but which is really a strong argument in favour of their analogy. It is

CHARACTERISTICS OF REFLEX AND INSTINCTIVE ACTIONS. 527

continually observed that when the stomach of the Polype is full, its arms do not make any attempt to seize objects that touch them; so that small worms, insects, &c., which would at other times be entrapped, may now come near them with impunity. It has been supposed that this results from an act of choice on the part of the animal, and that its choice is influenced by its consciousness that its stomach is supplied with food. It must seem improbable that an Animal which so nearly resembles Plants in its general habits, and in which the nervous system is so obscure that it has not yet been discovered, should possess mental endowments of so high a character; and we may find, in studying our own functions, a circumstance exactly parallel to that just mentioned. For when we commence eating, with a good appetite, we may notice that the muscles of Deglutition act very readily; but when we are completely satisfied, it is often difficult to excite these muscles to contraction, so as to swallow another morsel, even though, for the gratification of our palate, we may desire to do so. Thus we see how much better a guide we find in Nature, for the amount of food we require, than in our own pampered tastes.

694. The first class, that of Reflex movements, has been already considered in sufficient detail; but it is intended, in the present chapter, to offer some examples of those of the second and third classes,-those actions, namely, which are guided by Instinct and Intelligence respectively. These actions may be usually distinguished by the two following tests :1. Although, in most cases, experience is required to give the Will command over the muscles concerned in its operations, no experience or education is required, in order that the different actions which result from an Instinctive impulse may follow one another with unerring precision. 2. Instinctive actions are performed by the different individuals of the same species, nearly, if not exactly, in the same manner; presenting no such variation of the means applied to the objects in view, and admitting of no such improvements in the progress of life, or in the succession of ages, as we observe in the habits of individual Men, or in the manners and customs of nations, which are for the most part adapted to the attainment of particular ends, by voluntary efforts guided and directed by reason. Where, as in the examples hereafter to be men

[ocr errors]

528

DISTINCTIVE CHARACTERS OF INTELLIGENTIAL ACTIONS.

tioned (§ 717), we find individual animals "learning wisdom by experience," and acquiring the power of performing actions which do not correspond with their natural instincts, we cannot do otherwise than regard them as possessed of a certain degree of Intelligence, by which they are rendered susceptible of education.

695. The amount of Intelligence displayed in such acquirements, can only be judged-of, however, by carefully examining the circumstances under which they are made. If the new habits are gained-like the talking of a Parrot-by imitation simply, no great degree of intelligence is manifested; but if it spontaneously result from a reasoning process on the part of the animal, our idea of its sagacity is raised. There may be a combination of both these conditions; as in the following curious circumstance, related to the Author by a friend who has repeatedly witnessed it. Some horses kept in a paddock were supplied with water by a trough, which was occasionally filled from a pump,-not, however, as often as the horses seem to have wished; for one of them learned, of his own accord, to supply himself and his companions, by taking the pump-handle between his teeth, and working it with his head. The others, however, appear to have been less clever, or more lazy; and finding that this one had the power of supplying their wants, they would teaze him, by biting, kicking, &c., until he had pumped for them, and would not allow him to drink until they were satisfied. That this was not a mere act of imitation, appears from the circumstance that the horse did not attempt to imitate the movement of the man, but performed the same action in a different manner, evidently because it had associated in its mind the motion of the pumphandle with the supply of water.

race.

696. The Instincts of Animals may be shown to have immediate reference, probably in every instance, to the supply of the wants of the individual, or to the continuance of the Thus we have Instincts which guide in the selection and acquirement of food; others. which govern the construction of a habitation for the individual, and of a receptacle for the eggs,—and these may influence a number at once, in such a manner as to unite them into a society; and others which direct their migrations, whether in search of food, for the deposit of their eggs, or for other purposes. Of these, examples will now be given.

some

INSTINCT OF THE ANT-LION.

529

697. Among the instincts which direct animals in the acquirement of their food, few are more remarkable than those possessed by the larva of the Ant-lion (fig. 266), a small insect allied to the Dragon-fly. This larva (fig. 267) is destined to feed

Fig. 266.-ANT LION IN PERFECT STATE.

upon ants and other small insects, whose juices it sucks; but it moves slowly and with difficulty, so that it could scarcely have obtained the requisite supply of food, if Nature had not guided it in the construction of a remarkable snare, which entraps the prey it could not acquire by pursuit. It digs in fine sand a little funnel-shaped pit (fig. 268), and conceals

[graphic][merged small][subsumed]

itself at the bottom of this, until an insect falls over its edge; and if its victim seeks to escape, or stops in its fall to the bottom, it throws over it, by means of its head and mandibles, a quantity of sand, by which the insect is caused to roll down the steep, within reach of its captor. The manner in which

M M

« PreviousContinue »