Animal Intelligence Part 21

Similarly, those behind the point of interruption successively halted. After a pause of a few moments, the first caterpillar behind the break in the line endeavoured to fill up the vacant s.p.a.ce, and so recover contact or communication, which after a time it succeeded in doing, when the information that the line was again closed was pa.s.sed forward in some way from caterpillar to caterpillar till it reached the leader, when the whole fine was again put in motion.

The individual which had been abstracted remained rolled up and motionless; but on being placed near the moving column it immediately unrolled, and made every attempt to get readmitted into the procession. After many endeavours it succeeded, the one below falling into the rear of the interloper. On repeating the experiment by removing a caterpillar fifty from the head of the procession, Mr. Davis found that it took just thirty seconds by his watch for information of the fact to reach the leader. All the same results followed as in the previous case. It was observable that the animals were guided neither by sight nor smell while endeavouring to close up the interrupted line; for the caterpillar next behind the interruption, on whom the duty of closing up devolved, 'turned right and left, and often in a wrong direction, when within half an inch of the one immediately before him; when he at last touched the object of his search, the fact was communicated again by signal; and in thirty seconds the whole line was in rapid march.' This gentleman adds that the object of the march was the search for new pasture. The caterpillars feed on the Eucalyptus, and when they have completely stripped one tree of its leaves, they all congregate on the trunk, and proceed as described to another tree.

De Villiers[108] gives an account of his observations on the manner in which these caterpillars (_Cnethocampii pitzocampa_) are able to pa.s.s information, which does not quite agree with the above observation of Mr. Davis. For he says that, in a train of 600 caterpillars, interference by him in any part of the train was communicated through the whole series instantaneously--all the 600 caterpillars stopping immediately and with one consent like a single organism.

According to Kirby and Spence there is a kind of caterpillar (_Pieris crataegi_) which lives in little colonies of ten or twelve in common chambers lined with silk. In one part they make of the same material a little bag or pocket, which is used by the community or household as a water-closet. When full of excrement the caterpillars empty it by turning out the pellets with their feet.[109]

Only two other instances of noteworthy intelligence as exhibited by larvae have fallen within my reading. One of these is mentioned by Reaumur, who says that the larvae of _Hemerobius chrysops_ chase aphides, and having killed them, clothe themselves in their skins; and the other case is the very remarkable one mentioned in his newly published work by W. MacLachlan, F.R.S., of caddis-worms adjusting the specific gravity of their tubes to suit that of the water in which they live, by attaching heavy or light material to them according as they require sinking or flotation.

FOOTNOTES:

[90] Quoted by Bingley, _Animal Biography_, vol. iii., p. 118.

[91] _Loc. cit._, p. 344.

[92] Buchner, _loc. cit._, p. 344.

[93] Quoted in Strauss, _Insects_, s. 389.

[94] Kirby and Spence, _loc. cit._, pp. 321-2.

[95] _Life and Recollections_, vol. ii., p. 356.

[96] Quoted by Bingley, _loc. cit._, vol. iii., pp. 150-51.

[97] _Gleanings_, vol. ii., pp. 165-6.

[98] _American Journ. Sc. and Art_, vol. x., Oct. 1875.

[99] _Animal Biography_, vol. iii., pp. 244-5.

[100] _Nature_, vii., p. 49.

[101] _Intr. to Ent._, ii., p. 475.

[102] _Ibid._, p. 475.

[103] _[OE]uvres_, ix., p. 370.

[104] _Trans. Ent. Soc._, vol. ii.

[105] _Introd. Ent._, Letter xi.

[106] Westwood, _Trans. Ent. Soc._, vol. ii., p. 1.

[107] Kirby and Spence, _Entomology_, Letter xvi.

[108] _Trans. Ent. Soc. France_, vol. i., p. 201.

[109] _Introduction to Entomology_, Letter xxvi.

CHAPTER VIII.

FISH.

ALTHOUGH we here pa.s.s into the sub-kingdom of animals the intelligence of which immeasurably surpa.s.ses that of the other sub-kingdoms, it is remarkable that these lowest representatives of the higher group are psychologically inferior to some of the higher members of the lower groups. Neither in its instincts nor in general intelligence can any fish be compared with an ant or a bee--a fact which shows how slightly a psychological cla.s.sification of animals depends upon zoological affinity, or even morphological organisation. For although a highly competent authority, namely Van Baer, has said that a bee is as highly organised an animal as a fish, though on a different type,[110] no one would be found to a.s.sert that an ant or a bee is so much more highly organised than a fish as its higher intelligence would require, supposing degrees of intelligence to stand in necessary relation to degree of organic development. And this consideration is not materially altered if, instead of regarding the whole organism, we look to the nervous system alone. There is no doubt that the cerebral hemispheres of a fish, although small as compared with these organs in the higher Vertebrata, are, bulk for bulk, enormous as compared with the oesophageal ganglia or 'brain' of an insect; while the disproportion becomes still greater if the cerebral hemispheres of a fish are compared with their supposed a.n.a.logues in the brain of an ant, viz., the pedunculated and convoluted lobes which surmount the cephalic ganglion.

But here the relative smallness of the ant as a whole must be taken into consideration, and also the fact that its brain is relatively much more ma.s.sive as well as more highly organised than that which occurs in any other order of invertebrated animals, except, perhaps, the octopus and his allies. Therefore, although the brain of a fish is formed upon a type which by increase of size and complexity is destined in function far to eclipse all other types of nerve-centre, we have to observe that in its lowest stage of evolution as presented to science in the fishes, this type is functionally inferior to the invertebrate type, where this reaches its highest stage of evolution in the Hymenoptera.

_Emotions._

Fish display emotions of fear, pugnacity; social, s.e.xual, and parental feelings; anger, jealousy, play, and curiosity. So far the cla.s.s of emotions is the same as that with which we have met in ants, and corresponds with that which is distinctive of the psychology of a child about four months old. I have not, however, any evidence of sympathy, which would be required to make the list of emotions identical; but sympathy may nevertheless be present.

Fear and pugnacity are too apparent in fish to require special proof.

The social or gregarious feelings are strongly shown by the numberless species which swim in shoals, the s.e.xual feelings are proved by courtships, and the parental by those species which build nests and guard their young. Schneider saw several species of fish at the Naples Aquarium protecting their eggs. In one case the male mounted guard over a rock where the eggs were deposited, and swam with open mouth against intruders. The following accounts of the nidification of certain species of fish show that the parental instincts are not unlike those which obtain in birds, and are comparable in point of strength with the same instincts as they occur in ants, bees, and spiders.

Aga.s.siz remarks[111] that while examining the marine products of the Sarga.s.so Sea, Mr. Mansfield picked up and brought to him a round ma.s.s of sarga.s.sum, about the size of the two fists placed together. The whole consisted, to all appearance, of nothing but gulf-weed, the branches and leaves of which were, however, evidently knit together, and not merely balled into a roundish ma.s.s. The elastic threads which held the gulf-weed together were beaded at intervals, sometimes two or three beads being close together, or a branch of them hanging from the cl.u.s.ter of threads.

This nest was full of eggs scattered throughout the ma.s.s, and not placed together in a cavity. It was evidently the work of the _Chironectes_. This rocking fish-cradle is carried along as an undying arbour, affording at the same time protection and afterwards food for its living freight. It is suggested that the fish must have used their peculiar pectoral fins when constructing this elaborate nest.

The well-known tinker or ten-spined stickleback (_Gasterosteus pungitius_) is one of our indigenous fish which constructs a nest. On May 1, 1864, a male[112] was placed in a well-established aquarium of moderate size, to which, after three days, two ripe females were added. Their presence at once roused him into activity, and he soon began to build a nest of bits of dirt and dead fibre, and of growing confervoid filaments, upon a jutting point of rock among some interlacing branches of _Myriophyllum spicatum_--all the time, however, frequently interrupting his labours to pay his addresses to the females. This was done in most vigorous fashion, he swimming, by a series of little jerks, near and about the female, even pushing against her with open mouth, but usually not biting.

After a little coquetting she responds and follows him, swimming just above him as he leads the way to the nest. When there, the male commences to flirt--he seems unaware of its situation, will not swim to the right spot, and the female, after a few ineffectual attempts to find the proper pa.s.sage into it, turns tail to swim away, but is then viciously pursued by the male. When he first courts the female, if she, not being ready, does not soon respond, he seems quickly to lose his temper, and, attacking her with great apparent fury, drives her to seek shelter in some crevice or dark corner. The coquetting of the male near the nest, which seems due to the fact that he really has not quite finished it, at length terminates by his pushing his head well into the entrance of the nest, while the female closely follows him, placing herself above him, and apparently much excited. As he withdraws she pa.s.ses into the nest, and pushes quite through it, after a very brief delay, during which she deposits her ova. The male now fertilises the eggs, and drives the female away to a safe distance; then, after patting down the nest, he proceeds in search of another female. The nest is built and the ova deposited in about twenty-four hours. The male continued to watch it day and night, and during the light hours he also continually added to the nest.

The marine fifteen-spined stickleback (_Gasterosteus spinachia_) affords another instance of nest-constructing fishes. The places selected for their nests are usually harbours, or some sheltered spots to where pure sea water reaches. The fish either find growing, or even collect some of the softer kinds of green or red seaweed, and join them with so much of the coralline tufts (_Janiae_) growing on the rock as will serve the purpose of affording firmness to the structure, and const.i.tute a pear-shaped ma.s.s five or six inches long, and about as stout as a man's fist. A thread, which is elastic and resembles silk, is employed for the purpose of binding the materials together: under a magnifier it appears to consist of several strands connected by a gluey substance, which hardens by exposure to the water.[113]

M. Carbonnier, who has studied the habits of the Chinese b.u.t.terfly-fish (_Macropodus_) in his private aquarium in Paris, where he had some in confinement, observed that the male constructs a nest of froth of considerable size, 15 to 18 centimetres horizontal diameter, and 10 to 12 high. He prepares the bubbles in the air (which he sucks in and then expels), strengthening them with mucous matter from his mouth, and brings them into the nest. Sometimes the buccal secretion will fail him, whereupon he goes to the bottom in search of confervae, which he sucks and bites for a little in order to stimulate the act of secretion. The nest prepared, the female is induced to enter. Not less curious is the way in which the male brings the eggs from the bottom into the nest. He appears unable to carry them up in his mouth; instead of this, he first swallows an abundant supply of air, then descending, he places himself beneath the eggs, and suddenly, by a violent contraction of the muscles in the interior of his mouth and pharynx, he exhales the air which he had acc.u.mulated by the gills. This air, finely divided by the lamellae and fringes of the gills, escapes in the form of two jets of veritable gaseous powder, which envelopes the eggs and raises them to the surface. In this manoeuvre the _Macropodus_ entirely disappeared in a kind of air-mist, and when this had dissipated he reappeared with a mult.i.tude of air-bubbles like little pearls clinging all over his body.[1]

Again, in detailing Mr. Baker's observations on the three-spined stickleback, published in the Philosophical Transactions, this author says:--

It has been remarked that after the deposition of the eggs the nest was opened more to the action of the water, and the vibratory motion of the body of the male fish, hovering over its surface, caused a current of water to be propelled across the surface of the ova, which action was repeated almost continuously.

After about ten days the nest was destroyed and the materials removed; and now were seen the minute fry fluttering upwards here and there, by a movement half swimming, half leaping, and then falling rapidly again upon or between the clear pebbles of the shingle bottom. This arose from their having the remainder of the yelk still attached to their body, which, acting as a weight, caused them to sink the moment the swimming effort had ceased. Around, across, and in every direction the male fish, as the guardian, continually moved. Now his labours became more arduous, and his vigilance was taxed to the utmost extreme, for the other fish (two tench and a gold carp), some twenty times larger than himself, as soon as they perceived the young fry in motion, continuously used their utmost endeavours to snap them up. The courage of the little stickleback was now put to its severest test; but, nothing daunted, he drove them all off, seizing their fins and striking with all his strength at their heads and at their eyes. His care of the young brood when enc.u.mbered with the yelk was very extraordinary; and as this was gradually absorbed and they gained strength, their attempts to swim carried them to a greater distance from the parent fish; his vigilance, however, seemed everywhere, and if they rose by the action of their fins above a certain height from the shingle bottom, or flitted beyond a given distance from the nest, they were immediately seized in his mouth, brought back, and gently puffed or jetted into their place again.

The same care of the young, bringing them back to then nest up till about the sixth day after hatching, has been remarked by Dr. Ransom in the ten-spined stickleback (_G. pungitius_).[114]

The well-known habit of the lophobranchiate fish, of incubating their eggs in their pouches, also displays highly elaborated parental feeling.[115] M. Risso says that when the young of the pipe-fish are hatched out, the parents show them marked attachment, and that the pouch then serves them as a place of shelter or retreat from danger.[116]

M. Carbonnier has recorded how the male of the curiously grotesque telescope-fish, a variety of _Cara.s.sius auratus_ (Linn.), acts as accoucheur to the female. Three males pursued one female which was heavy with sp.a.w.n, and rolled her like a ball upon the ground for a distance of several metres, and continued this process without rest or relaxation for two days, until the exhausted female, who had been unable to recover her equilibrium for a moment, had at last evacuated all her ova.[117]

That adult fish are capable of feeling affection for one another would seem to be well established: thus Jesse relates how he once captured a female pike (_Esox lucius_) during the breeding season, and that nothing could drive away the male from the spot at which he had perceived his partner slowly disappear, and whom he had followed to the edge of the water.

Mr. Arderon[118] gave an account of how he tamed a dace, which would lie close to the gla.s.s watching its master; and subsequently how he kept two ruffs (_Acerina cernua_) in an aquarium, where they became very much attached to one another. He gave one away, when the other became so miserable that it would not eat, and this continued for nearly three weeks.

Fearing his remaining fish might die, he sent for its former companion, and on the two meeting they became quite happy again. Jesse gives a similar account of two gold carp.[119]

Anger is strikingly shown by many fish, and notoriously by sticklebacks when their territory is invaded by a neighbour. These animals display a strange instinct of appropriating to themselves a certain part of the tank in which they may be confined, and furiously attacking any other stickleback which may presume to cross the imaginary frontier. Under such circ.u.mstances of provocation I have seen the whole animal change colour, and, darting at the trespa.s.ser, show rage and fury in every movement. Of course, here, as elsewhere, it is impossible to be sure how far apparent expression of an emotion is due to the presence of that mental state which we recognise as the emotion in ourselves; but still the best guide we have to follow is that of apparent expression.