Animal Intelligence Part 2

[8] _Natural History of Ceylon_, p. 481.

CHAPTER II.

MOLLUSCA.

I SHALL treat of the Mollusca before the Articulata, because as a group their intelligence is not so high. Indeed, it is not to be expected that the cla.s.s of animals wherein the 'vegetative' functions of nutrition and reproduction predominate so largely over the animal functions of sensation, locomotion, &c., should present any considerable degree of intelligence. Nevertheless, in the only division of the group which has sense organs and powers of locomotion highly developed--viz., the Cephalopoda--we meet with large cephalic ganglia, and, it would appear, with no small development of intelligence. Taking, however, the sub-kingdom in ascending order, I shall first present all the trustworthy evidence that I have been able to collect, pointing to the highest level of intelligence that is attained by the lower members.

The following is quoted from Mr. Darwin's MS.:--

Even the headless oyster seems to profit from experience, for Dicquemase ('Journal de Physique,'

vol. xxviii. p. 244) a.s.serts that oysters taken from a depth never uncovered by the sea, open their sh.e.l.ls, lose the water within, and perish; but oysters taken from the same place and depth, if kept in reservoirs, where they are occasionally left uncovered for a short time, and are otherwise incommoded, learn to keep their sh.e.l.ls shut, and then live for a much longer time when taken out of the water.[9]

Some evidence of intelligence seems to be displayed by the razor-fish.

For the animals dislike salt, so that when this is sprinkled above their burrows in the sand, they come to the surface and quit their habitations. But if the animal is once seized when it comes to the surface and afterwards allowed to retire into its burrow, no amount of salt will force it again to come to the surface.[10]

With regard to snails, L. Aga.s.siz writes: 'Quiconque a eu l'occasion d'observer les amours des limacons, ne saurait mettre en doute la seduction deployee dans les mouvements et les allures qui preparent et accomplissent le double embra.s.s.e.m.e.nt de ces hermaphrodites.'[11]

Again, Mr. Darwin's MS. quotes from Mr. W. White[12] a curious exhibition of intelligence in a snail, which does not seem to have admitted of mal-observation. This gentleman 'fixed a land-sh.e.l.l mouth uppermost in a c.h.i.n.k of rock; in a short time the snail protruded itself to its utmost length, and, attaching its foot vertically above, tried to pull the sh.e.l.l out in a straight line. Not succeeding, it rested for a few minutes and then stretched out its body on the right side and pulled its utmost, but failed. Resting again, it protruded its foot on the left side, pulled with its full force, and freed the sh.e.l.l. This exertion of force in three directions, which seems so geometrically suitable, must have been intentional.'

If it is objected that snail sh.e.l.ls must frequently be liable to be impeded by obstacles, and therefore that this display of manoeuvring on the part of their occupants is to be regarded as a reflex, I may remark that here again we have one of those incessantly recurring cases where it is difficult to draw the line between intelligence and non-intelligence. For, granting that the action is to a certain extent mechanical, we must still recognise that the animal while executing it must have remembered each of the two directions in which it had pulled ineffectually before it began to pull in the third direction; and it is improbable that snail sh.e.l.ls are so frequently caught in positions from which a pull in only one direction will release them, that natural selection would have developed a special instinct to try pulling successively in three directions at right angles to one another.

The only other instance that I have met with of the apparent display of intelligence in snails is the remarkable one which Mr. Darwin gives in his 'Descent of Man,' on the authority of Mr. Lonsdale. Although the interpretation which is a.s.signed to the fact seems to me to go beyond anything that we should have reason to expect of snail intelligence, I cannot ignore a fact which stands upon the observation of so good an authority, and shall therefore quote it in Mr. Darwin's words:--

These animals appear also susceptible of some degree of permanent attachment: an accurate observer, Mr.

Lonsdale, informs me that he placed a pair of land-snails (_Helix pomatia_), one of which was weakly, into a small and ill-provided garden. After a short time the strong and healthy individual disappeared, and was traced by its track of slime over a wall into an adjoining well-stocked garden. Mr.

Lonsdale concluded that it had deserted its sickly mate; but after an absence of twenty-four hours it returned, and apparently communicated the result of its successful exploration, for both then started along the same track, and disappeared over the wall.[13]

In this case the fact must be accepted, seeing that it stands on the authority of an accurate observer, and is of so definite a kind as not to admit of mistake. Consequently we are shut up to the alternative of supposing the return of the healthy snail to its mate a mere accident, and their both going over the wall into the well-stocked garden another mere accident, or acquiescing in the interpretation which Mr. Darwin a.s.signs. Now, if we look closely into the matter, the chances against the double accident in question are certainly so considerable as to render the former supposition almost impossible. On the other hand, there is evidence to prove, as I shall immediately show, that a not distantly allied animal is unquestionably able to remember a particular locality as its home, and habitually to return to this locality after feeding. Therefore, in view of this a.n.a.logous and corroborative case, the improbability of the snail remembering for twenty-four hours the position of its mate is very much reduced; while the subsequent communication, if it took place, would only require to have been of the nature of 'follow me,' which, as we shall repeatedly find, is a degree of communicative ability which many invertebrated animals possess.

Therefore, in view of these considerations, I incline to Mr. Darwin's opinion that the facts can only be explained by supposing them due to intelligence on the part of the snails. Thus considered, these facts are no doubt very remarkable; for they would appear to indicate not merely accurate memory of direction and locality for twenty-four hours, but also no small degree of something akin to 'permanent attachment,' and sympathetic desire that another should share in the good things which one has found.[14]

The case to which I have just alluded as proving beyond all doubt that some Gasteropoda are able to retain a very precise and accurate memory of locality, is that of the common limpet.

Mr. J. Clarke Hawkshaw publishes in the Journal of the Linnaean Society the following account of the habits in question:--

The holes in the chalk in which the limpets are often to be found are, I believe, excavated in a great measure by rasping from the lingual teeth, though I doubt whether the object is to form a cavity to shelter in, though the cavities, when formed, may be of use for that purpose. It must be of the greatest importance to a limpet that, in order that it may insure a firm adherence to the rock, its sh.e.l.l should fit the rock accurately; when the sh.e.l.l does fit the rock accurately, a small amount of muscular contraction of the animal would cause the sh.e.l.l to adhere so firmly to a smooth surface as to be practically immoveable without fracture. As the sh.e.l.ls cannot be adapted daily to different forms of surface, the limpets generally return to the same place of attachment. I am sure this is the case with many; for I found sh.e.l.ls perfectly adjusted to the uneven surfaces of flints, the growth of the sh.e.l.ls being in some parts distorted and indented to suit inequalities in the surface of the flints... .

I noticed signs that limpets prefer a hard, smooth surface to a pit in the chalk. On one surface of a large block, over all sides of which limpets were regularly and plentifully distributed, there were two flat fragments of a fossil sh.e.l.l about 3 inches by 4 inches, each embedded in the chalk. The chalk all round these fragments was free from limpets; but on the smooth surface of the pieces of sh.e.l.l they were packed as closely as they could be. I noticed another case, which almost amounts, to my mind, to a proof that they prefer a smooth surface to a hole. A limpet had formed a clearing on one of the sea-weed-covered blocks before referred to. In the midst of this clearing was a pedestal of flint rather more than one inch in diameter, standing up above the surface of the chalk; it projected so much that a tap from my hammer broke it off. On the top of the smooth fractured surface of this flint the occupant of the clearing had taken up its abode. The sh.e.l.l was closely adapted to the uneven surface, which it would only fit in one position. The cleared surface was in a hollow with several small natural cavities, where the limpet could have found a pit ready made to shelter in; yet it preferred, after each excursion, to climb up to the top of the flint, the most exposed point in all its domain.[15]

It appears certain from these observations, which to some extent were antic.i.p.ated by those of Mr. F. C. Lukis,[16] that limpets, after every browsing excursion, return to one particular spot or home; and the precise memory of direction and locality implied by this fact seems to justify us in regarding these actions of the animal as of a nature unquestionably intelligent.

Coming now to the cephalopoda, there is no doubt that if a larger sphere of opportunity permitted, adequate observation of these animals would prove them to be much the most intelligent members of the sub-kingdom.

Unfortunately, however, this sphere of opportunity has. .h.i.therto been very limited. The following meagre account is all that I have been able to gather concerning the psychology of these interesting animals.

According to Schneider,[17] the Cephalopoda show unmistakable evidence of consciousness and intelligence. This observer had an opportunity of watching them for a long time in the zoological station at Naples; and he says that they appeared to recognise their keeper after they had for some time received their food from him. Hollmann narrates that an octopus, which had had a struggle with a lobster, followed the latter into an adjacent tank, to which it had been removed for safety, and there destroyed it. In order to do this the octopus had to climb up a vertical part.i.tion above the surface of the water and descend the other side.[18] According to Schneider, the Cephalopoda have an abstract idea of water, seeking to return to it when removed, even though they do not see it. But this probably arises from the sense of discomfort due to exposure of their skin to the air; and if we can call it an 'idea,' it is doubtless shared by all other aquatic Mollusca when exposed to air.

FOOTNOTES:

[9] This fact is also stated by Bingley, _Animal Biography_, vol. iii.

p. 454, and is now turned to practical account in the so-called 'Oyster-schools' of France. The distance from the coast to Paris being too great for the newly dredged oysters to travel without opening their sh.e.l.ls, they are first taught in the schools to bear a longer and longer exposure to the air without gaping, and when their education in this respect is completed they are sent on their journey to the metropolis, where they arrive with closed sh.e.l.ls, and in a healthy condition.

[10] Bingley, _loc. cit._, vol. iii. p. 449.

[11] _De l'Espece et de la Cla.s.se_, &c., 1869, p. 106.

[12] _A Londoner's Walk to Edinburgh_, p. 155 (1856).

[13] _Descent of Man_, pp. 262-3.

[14] The facts, however, in order to sustain such conclusions, of course require corroboration, and it is therefore to be regretted that Mr.

Lonsdale did not experimentally repeat the conditions.

[15] _Journal Linn. Soc._ vol. xiv. p. 406 _et seq._

[16] _Mag. Nat. Hist._ 1831, vol. iv. p. 346.

[17] _Thieresche Wille_, -- 78.

[18] _Leben der Cephalopoden_, s. 21.

CHAPTER III.

ANTS.

WITHIN the last ten or twelve years our information on the habits and intelligence of these insects has been so considerably extended, that in here rendering a condensed epitome of our knowledge in this most interesting branch of comparative psychology, it will be found that the chapter is const.i.tuted princ.i.p.ally of a statement of observations and experiments which have been conducted during the short period named. The observers to whom we are mainly indebted for this large increase of our knowledge are Messrs. Bates, Belt, Muller, Moggridge, Lincec.u.m, MacCook, and Sir John Lubbock. From the fact that these naturalists conducted their observations in different parts of the world and on widely different species of ants, it is not surprising that their results should present many points of difference; for this only shows, as we might have expected, that different species of ants differ considerably in habits and intelligence. Therefore, in now drawing all these numerous observations to a focus, I shall endeavour to show clearly their points of difference as well as their points of agreement; and in order that the facts to be considered may be arranged in some kind of order, I shall deal with them under the following heads:--Powers of special sense; Sense of direction; Powers of memory; Emotions; Powers of communication; Habits general in sundry species; Habits peculiar to certain species; General intelligence of various species.

_Powers of Special Sense._

Taking first the sense of sight, Sir John Lubbock made a number of experiments on the influence of light coloured by pa.s.sing through various tints of stained gla.s.s, with the following results. The ants which he observed greatly dislike the presence of light within their nests, hurrying about in search of the darkest corners when light is admitted. The experiments showed that the dislike is much greater in the case of some colours than in that of others. Thus under a slip of red gla.s.s there were congregated on one occasion 890 ants, under green 544, under yellow 495, and under violet only 5. To our eyes the violet is as opaque as the red, more so than the green, and much more so than the yellow. Yet, as the numbers show, the ants had scarcely any tendency to congregate under it: there were nearly as many under the same area of the uncovered portion of the nest as under that shaded by the violet gla.s.s. It is curious that the coloured gla.s.ses appear to act on the ants in a graduated series, which corresponds with the order of their influence on a photographic plate. Experiments were therefore made to test whether it might not be the actinic rays that were so particularly distasteful to the ants; but with negative results. Placing violet gla.s.s above red produces the same effect as red gla.s.s alone. Obviously, therefore, the ants avoid the violet gla.s.s because they dislike the rays which it transmits, and do not prefer the other colours because they like the rays which they transmit. Sodium, barium, strontium, and lithium flames were also tried, but not with so much effect as the coloured gla.s.s.

It has just been observed that the relative dislike which Sir John Lubbock's ants showed to lights of different colours seems to be determined by the position of the colour in the spectrum--there being a regular gradation of intolerance shown from the red to the violet end.

As these ants dislike light, the question suggests itself that the reason of their graduated intolerance to light of different colours may be due to their eyes not being so much affected by the rays of low as by those of high refrangibility. In this connection it would be interesting to ascertain whether ants of the genus _Atta_ show a similarly graduated intolerance to the light in different parts of the spectrum; for both Moggridge and MacCook record of this genus that it not only does not shun the light, but seeks it--coming to the gla.s.s sides of their artificial nests to enjoy the light of a lamp. Possibly, therefore, the scale of preference to lights of different colours would be found in this genus to be the reverse of that which Sir John Lubbock has found in the case of the British species.

As regards hearing, Sir John Lubbock found that sounds of various kinds do not produce any effect upon the insects. Tuning-forks and violin notes, shouting, whistling, &c., were all equally inefficient in producing the slightest influence upon the animals; and experiments with sensitive flames, microphone, telephone, &c., failed to yield any evidence of ants emitting sounds inaudible to human ears.

Lastly, as regards the sense of smell, Sir John Lubbock found that on bringing a camel's-hair brush steeped in various strong scents near where ants were pa.s.sing, "some went on without taking any notice, but others stopped, and evidently perceiving the smell, turned back. Soon, however, they returned, and pa.s.sed the scented pencil. After doing this two or three times, they generally took no further notice of the scent.

This experiment left no doubt on my mind." In other cases the ants were observed to wave about and throw back their antennae when the scented pencil was brought near.

That ants track one another by scent was long ago mentioned by Huber, and also that they depend on this sense for their power of finding supplies which have been previously found by other ants. Huber proved their power of tracking a path previously pursued by their friends, by drawing his finger across the trail, so obliterating the scent at that point, and observing that when the ants arrived at that point they became confused and ran about in various directions till they again came upon the trail on the other side of the interrupted s.p.a.ce, when they proceeded on their way as before. The more numerous and systematic experiments of Sir John Lubbock have fully corroborated Huber's observations, so far as these points are concerned. Thus, to give only one or two of these experiments; in the accompanying woodcut (Fig. 1) A is the nest, B a board, _n_ _f_ _g_ slips of paper, _h_ and _m_ similar slides of gla.s.s, on one of which, _h_, there was placed pupae, while the other, _m_, was left empty. Sir John Lubbock watched two particular (marked) ants proceeding from A to _h_ and back again, carrying the pupae on _h_ to the nest A. Whenever an ant came out of A upon B he transposed the slips _f_ and _g_. Therefore at the angle below _n_ there was a choice presented to the ant of taking the unscented pathway leading to the full gla.s.s _h_, or the scented pathway leading to the empty gla.s.s _m_. The two marked ants, knowing their way, always took the right turn at the angle; but the stranger ants, being guided only by scent, for the most part took the wrong turn at the angle, so going to the empty gla.s.s _m_. For out of 150 stranger ants only 21 went to _h_, while the remaining 129 went to _m_. Still the fact that all the stranger ants did not follow the erroneous scent-trail to _m_, may be taken to indicate that they are also a.s.sisted in finding treasure by the sense of sight, though in a lesser degree. Therefore Sir John Lubbock concludes that in finding treasure 'they are guided in some cases by sight, while in others they track one another by scent.'