Part 42

field. It is questionable, however, whether this holds good in civilized warfare. Colours were carried in action by both the Russians and the Japanese in the war of 1904-5, and they were supplemented on both sides by smaller flags or camp colours. The conception of the colour as the emblem of union, the rallying-point, of the regiment has been mentioned above. Many hold that such a rallying-point is more than ever required in the modern _guerre de masses_, when a national short-service army is collected in all possible strength on the decisive battle-field, and that scarcely any risks or loss of life would be disproportionate to the advantages gained by the presence of the colours. There is further a most important factor in the problem, which has only arisen in recent years through modern perfection in armament. In the first stages of an attack, the colours could remain, as in the past, with the closed reserves or line of battle, and they would not be uncased and sent into the thick of the fight at all hazards until the decisive assault was being delivered. Then, it is absolutely essential, as a matter of tactics, that the artillery (q.v.), which covers the assault with all the power given it by modern science and training, should be well informed as to the progress of the infantry. This covering fire was maintained by the Japanese until the infantry was actually in the smoke of their own shrapnel. With uniforms of neutral tint the need of some means whereby the artillery officers can, at 4000 yds. range, distinguish their own infantry from that of the enemy, is more pronounced than ever. The best troops are apt to be unsteadied by being fired into by their own guns (e.g. at Elandslaagte), and the more powerful the shell, and the more rapid and far-ranging the fire of the guns, the more necessary it becomes to prevent such accidents. A practicable solution of the difficulty would be to display the colours as of old, and this course would not only have to an enhanced degree the advantages it formerly possessed, but would also provide the simplest means for ensuring the vitally necessary co-operation of infantry and artillery in the decisive assault. The duty of carrying the colours was always one of special danger, and sometimes, in the old short-range battles, every officer who carried a flag was shot. That this fate would necessarily overtake the bearer under modern conditions is far from certain, and in any case the few men on the enemy's side who would be brave enough to shoot accurately under heavy shell fire would, however destructive to the colour party, scarcely inflict as much damage on the battalion as a whole, as a dozen or more accidental shells from the massed artillery of its own side.

COLOUR-SERGEANT, a non-commissioned officer of infantry, ranking, in the British army, as the senior non-commissioned officer of each company. He is charged with many administrative duties, and usually acts as pay sergeant. A special duty of the colour-sergeants of a battalion is that of attending and guarding the colours and the officers carrying them. In some foreign armies the colours are actually carried by colour-sergeants. The rank was created in the British army in 1813.

COLOURS OF ANIMALS. Much interest attaches in modern biology to the questions involved in the colours of animals. The subject may best be considered in two divisions: (1) as regards the uses of colour in the struggle for existence and in sexual relationships; (2) as regards the chemical causation.

1. BIONOMICS

_Use of Colour for Concealment._--_Cryptic colouring_ is by far the commonest use of colour in the struggle for existence. It is employed for the purpose of attack (_aggressive resemblance_ or _anticryptic colouring_) as well as of defence (_protective resemblance_ or _procryptic colouring_). The fact that the same method, concealment, may be used both for attack and defence has been well explained by T. Belt (_The Naturalist in Nicaragua_, London, 1888), who suggests as an illustration the rapidity of movement which is also made use of by both pursuer and pursued, which is similarly raised to a maximum in both by the gradual dying out of the slowest through a series of generations. Cryptic colouring is commonly associated with other aids in the struggle for life. Thus well-concealed mammals and birds, when discovered, will generally endeavour to escape by speed, and will often attempt to defend themselves actively. On the other hand, small animals which have no means of active defence, such as large numbers of insects, frequently depend upon concealment alone. Protective resemblance is far commoner among animals than aggressive resemblance, in correspondence with the fact that predaceous forms are as a rule much larger and much less numerous than their prey. In the case of insectivorous Vertebrata and their prey such differences exist in an exaggerated form. Cryptic colouring, whether used for defence or attack, may be either _general_ or _special_. In _general resemblance_ the animal, in consequence of its colouring, produces the same effect as its environment, but the conditions do not require any special adaptation of shape and outline. General resemblance is especially common among the animals inhabiting some uniformly coloured expanse of the earth's surface, such as an ocean or a desert. In the former, animals of all shapes are frequently protected by their transparent blue colour; on the latter, equally diverse forms are defended by their sandy appearance. The effect of a uniform appearance may be produced by a combination of tints in startling contrast. Thus the black and white stripes of the zebra blend together at a little distance, and "their proportion is such as exactly to match the pale tint which arid ground possesses when seen by moonlight" (F. Galton, _South Africa_, London, 1889). _Special resemblance_ is far commoner than general, and is the form which is usually met with on the diversified surface of the earth, on the shores, and in shallow water, as well as on the floating masses of Algae on the surface of the ocean, such as the Sargasso Sea. In these environments the cryptic colouring of animals is usually aided by special modifications of shape, and by the instinct which leads them to assume

## particular attitudes. Complete stillness and the assumption of a certain

attitude play an essential part in general resemblance on land; but in special resemblance the attitude is often highly specialized, and perhaps more important than any other element in the complex method by which concealment is effected. In special resemblance the combination of colouring, shape and attitude is such as to produce a more or less exact resemblance to some one of the objects in the environment, such as a leaf or twig, a patch of lichen, or flake of bark. In all cases the resemblance is to some object which is of no interest to the enemy or prey respectively. The animal is not hidden from view by becoming indistinguishable from its background, as in the cases of general resemblance, but it is mistaken for some well-known object.

In seeking the interpretation of these most interesting and elaborate adaptations, attempts have been made along two lines. First, it is sought to explain the effect as a result of the direct influence of the environment upon the individual (G. L. L. Buffon), or by the inherited effects of effort and the use and disuse of parts (J. B. P. Lamarck). Second, natural selection is believed to have produced the result, and afterwards maintained it by the survival of the best concealed in each generation. The former suggestions break down when the complex nature of numerous special resemblances is appreciated. Thus the arrangement of colours of many kinds into an appropriate pattern requires the co-operation of a suitable shape and the rigidly exact adoption of a certain elaborate attitude. The latter is instinctive, and thus depends on the central nervous system. The cryptic effect is due to the exact co-operation of all these factors; and in the present state of science the only possible hope of an interpretation lies in the theory of natural selection, which can accumulate any and every variation which tends towards survival. A few of the chief types of methods by which concealment is effected may be briefly described. The colours of large numbers of Vertebrate animals are darkest on the back, and become gradually lighter on the sides, passing into white on the belly. Abbott H. Thayer (_The Auk_, vol. xiii., 1896) has suggested that this gradation obliterates the appearance of solidity, which is due to shadow. The colour-harmony, which is also essential to concealment, is produced because the back is of the same tint as the environment (_e.g._ earth) bathed in the cold blue-white of the sky, while the belly, being cold blue-white bathed in shadow and yellow earth reflections, produces the same effect. Thayer has made models (in the natural history museums at London, Oxford and Cambridge) which support his interpretation in a very convincing manner. This method of neutralizing shadow for the purpose of concealment by increased lightness of tint was first suggested by E. B. Poulton in the case of a larva (_Trans. Ent. Soc. Lond._, 1887, p. 294) and a pupa (_Trans. Ent. Soc. Lond._, 1888, pp. 596, 597), but he did not appreciate the great importance of the principle. In an analogous method an animal in front of a background of dark shadow may have part of its body obliterated by the existence of a dark tint, the remainder resembling, e.g., a part of a leaf (W. Müller, _Zool. Jahr. J. W. Spengel_, Jena, 1886). This method of rendering invisible any part which would interfere with the resemblance is well known in mimicry. A common aid to concealment is the adoption by different individuals of two or more different appearances, each of which resembles some special object to which an enemy is indifferent. Thus the leaf-like butterflies (_Kallima_) present various types of colour and pattern on the under side of the wings, each of which closely resembles some well-known appearance presented by a dead leaf; and the common British yellow under-wing moth (_Tryphaena pronuba_) is similarly polymorphic on the upper side of its upper wings, which are exposed as it suddenly drops among dead leaves. Caterpillars and pupae are also commonly _dimorphic_, green and brown. Such differences as these extend the area which an enemy is compelled to search in order to make a living. In many cases the cryptic colouring changes appropriately during the course of an individual life, either seasonally, as in the ptarmigan or Alpine hare, or according as the individual enters a new environment in the course of its growth (such as larva, pupa, imago, &c.). In insects with more than one brood in the year, _seasonal dimorphism_ is often seen, and the differences are sometimes appropriate to the altered condition of the environment as the seasons change. The causes of change in these and Arctic animals are insufficiently worked out: in both sets there are observations or experiments which indicate changes from within the organism, merely following the seasons and not caused by them, and other observations or experiments which prove that certain species are susceptible to the changing external influences. In certain species concealment is effected by the use of adventitious objects, which are employed as a covering. Examples of this _allocryptic_ defence are found in the tubes of the caddis worms (_Phryganea_), or the objects made use of by crabs of the genera _Hyas_, _Stenorhynchus_, &c. Such animals are concealed in any environment. If sedentary, like the former example, they are covered up with local materials; if wandering, like the latter, they have the instinct to reclothe. Allocryptic methods may also be used for aggressive purposes, as the ant-lion larva, almost buried in sand, or the large frog _Ceratophrys_, which covers its back with earth when waiting for its prey. Another form of allocryptic defence is found in the use of the colour of the food in the digestive organs showing through the transparent body, and in certain cases the adventitious colour may be dissolved in the blood or secreted in superficial cells of the body: thus certain insects make use of the chlorophyll of their food (Poulton, _Proc. Roy. Soc._ liv. 417). The most perfect cryptic powers are possessed by those animals in which the individuals can change their colours into any tint which would be appropriate to a normal environment. This power is widely prevalent in fish, and also occurs in Amphibia and Reptilia (the chameleon affording a well-known example). Analogous powers exist in certain Crustacea and Cephalopoda. All these rapid changes of colour are due to changes in shape or position of superficial pigment cells controlled by the nervous system. That the latter is itself stimulated by light through the medium of the eye and optic nerve has been proved in many cases. Animals with a short life-history passed in a single environment, which, however, may be very different in the case of different individuals, may have a different form of _variable cryptic colouring_, namely, the power of adapting their colour once for all (many pupae), or once or twice (many larvae). In these cases the effect appears to be produced through the nervous system, although the stimulus of light probably acts on the skin and not through the eyes. Particoloured surfaces do not produce particoloured pupae, probably because the antagonistic stimuli neutralize each other in the central nervous system, which then disposes the superficial colours so that a neutral or intermediate effect is produced over the whole surface (Poulton, _Trans. Ent. Soc. Lond._, 1892, p. 293). Cryptic colouring may incidentally produce superficial resemblances between animals; thus desert forms concealed in the same way may gain a likeness to each other, and in the same way special resemblances, e.g. to lichen, bark, grasses, pine-needles, &c., may sometimes lead to a tolerably close similarity between the animals which are thus concealed. Such likeness may be called _syncryptic_ or _common protective_ (or _aggressive_) _resemblance_, and it is to be distinguished from mimicry and common warning colours, in which the likeness is not incidental, but an end in itself. Syncryptic resemblances have much in common with those incidentally caused by functional adaptation, such as the mole-like forms produced in the burrowing Insectivora, Rodentia and Marsupialia. Such likeness may be called _syntechnic resemblance_, incidentally produced by dynamic similarity, just as syncryptic resemblance is produced by static similarity.

_Use of Colour for Warning and Signalling, or Sematic Coloration._--The use of colour for the purpose of warning is the exact opposite of the one which has been just described, its object being to render the animal conspicuous to its enemies, so that it can be easily seen, well remembered, and avoided in future. Warning colours are associated with some quality or weapon which renders the possessor unpleasant or dangerous, such as unpalatability, an evil odour, a sting, the poison-fang, &c. The object being to warn an enemy off, these colours are also called _aposematic_. Recognition markings, on the other hand, are _episematic_, assisting the individuals of the same species to keep together when their safety depends upon numbers, or easily to follow each other to a place of safety, the young and inexperienced benefiting by the example of the older. Episematic characters are far less common than aposematic, and these than cryptic; although, as regards the latter comparison, the opposite impression is generally produced from the very fact that concealment is so successfully attained. Warning or aposematic colours, together with the qualities they indicate, depend, as a rule, for their very existence upon the abundance of palatable food supplied by the animals with cryptic colouring. Unpalatability, or even the possession of a sting, is not sufficient defence unless there is enough food of another kind to be obtained at the same time and place (Poulton, _Proc. Zool. Soc._, 1887, p. 191). Hence insects with warning colours are not seen in temperate countries except at the time when insect life as a whole is most abundant; and in warmer countries, with well-marked wet and dry seasons, it will probably be found that warning colours are proportionately less developed in the latter. In many species of African butterflies belonging to the genus _Junonia_ (including _Precis_) the wet-season broods are distinguished by the more or less conspicuous under sides of the wings, those of the dry season being highly cryptic. Warning colours are, like cryptic, assisted by special adaptations of the body-form, and especially by movements which assist to render the colour as conspicuous as possible. On this account animals with warning colours generally move or fly slowly, and it is the rule in butterflies that the warning patterns are similar on both upper and under sides of the wings. Many animals, when attacked or disturbed, "sham death" (as it is commonly but wrongly described), falling motionless to the ground. In the case of well-concealed animals this instinct gives them a second chance of escape in the earth or among the leaves, &c., when they have been once detected; animals with warning colours are, on the other hand, enabled to assume a position in which their characters are displayed to the full (J. Portschinsky, _Lepidopterorum Rossiae Biologia_, St Petersburg, 1890, plate i. figs. 16, 17). In both cases a definite attitude is assumed, which is not that of death. Other warning characters exist in addition to colouring: thus sound is made use of by the disturbed rattlesnake and the Indian _Echis_, &c. Large birds, when attacked, often adopt a threatening attitude, accompanied by a terrifying sound. The cobra warns an intruder chiefly by attitude and the dilation of the flattened neck, the effect being heightened in some species by the "spectacles." In such cases we often see the combination of cryptic and sematic methods, the animal being concealed until disturbed, when it instantly assumes an aposematic attitude. The advantage to the animal itself is clear: a poisonous snake gains nothing by killing an animal it cannot eat; while the poison does not cause immediate death, and the enemy would have time to injure or destroy the snake. In the case of small unpalatable animals with warning colours the enemies would only first become aware of the unpleasant quality by tasting and often destroying their prey; but the species would gain by the experience thus conveyed, even though the individual might suffer. An insect-eating animal does not come into the world with knowledge: it has to be educated by experience, and warning colours enable this education as to what to avoid to be gained by a small instead of a large waste of life. Furthermore, great tenacity of life is usually possessed by animals with warning colours. The tissues of aposematic insects generally possess great elasticity and power of resistance, so that large numbers of individuals can recover after very severe treatment.

The brilliant warning colours of many caterpillars attracted the attention of Darwin when he was thinking over his hypothesis of sexual selection, and he wrote to A. R. Wallace on the subject (C. Darwin, _Life and Letters_, London, 1887, iii. 93). Wallace, in reply, suggested their interpretation as warning colours, a suggestion since verified by experiment (_Proc. Ent. Soc. Lond._, 1867, p. lxxx; _Trans. Ent. Soc. Lond._, 1869, pp. 21 and 27). Although animals with warning colours are probably but little attacked by the ordinary enemies of their class, they have special enemies which keep the numbers down to the average. Thus the cuckoo appears to be an insectivorous bird which will freely devour conspicuously coloured unpalatable larvae. The effect of the warning colours of caterpillars is often intensified by gregarious habits. Another aposematic use of colours and structures is to divert attention from the vital parts, and thus give the animal attacked an extra chance of escape. The large, conspicuous, easily torn wings of butterflies and moths act in this way, as is found by the abundance of individuals which may be captured with notches bitten symmetrically out of both wings when they were in contact. The eye-spots and "tails" so common on the hinder part of the hind wing, and the conspicuous apex so frequently seen on the fore wing, probably have this meaning. Their position corresponds to the parts which are most offen found to be notched. In some cases (e.g. many _Lycaenidae_) the "tail" and eye-spot combine to suggest the appearance of a head with antennae at the posterior end of the butterfly, the deception being aided by movements of the hind wings. The flat-topped "tussocks" of hair on many caterpillars look like conspicuous fleshy projections of the body, and they are held prominently when the larva is attacked. If seized, the "tussock" comes out, and the enemy is greatly inconvenienced by the fine branched hairs. The tails of lizards, which easily break off, are to be similarly explained, the attention of the pursuer being probably still further diverted by the extremely active movements of the amputated member. Certain crabs similarly throw off their claws when attacked, and the claws continue to snap most actively. The tail of the dormouse, which easily comes off, and the extremely bushy tail of the squirrel, are probably of use in the same manner. Animals with warning colours often tend to resemble each other superficially. This fact was first pointed out by H. W. Bates in his paper on the theory of mimicry (_Trans. Linn. Soc._ vol. xxiii., 1862, p. 495). He showed that the conspicuous, presumably unpalatable, tropical American butterflies, belonging to very different groups, which are mimicked by others, also tend to resemble each other, the likeness being often remarkably exact. These resemblances were not explained by his theory of mimicry, and he could only suppose that they had been produced by the direct influence of a common environment. The problem was solved in 1879 by Fritz Müller (see _Proc. Ent. Soc. Lond._, 1879, p. xx.), who suggested that life is saved by this resemblance between warning colours, inasmuch as the education of young inexperienced enemies is facilitated. Each species which falls into a group with common warning (_synaposematic_) colours contributes to save the lives of the other members. It is sufficiently obvious that the amount of learning and remembering, and consequently of injury and loss of life involved in the process, are reduced when many species in one place possess the same aposematic colouring, instead of each exhibiting a different "danger-signal." These resemblances are often described as "Müllerian mimicry," as distinguished from true or "Batesian mimicry" described in the next section. Similar synaposematic resemblances between the specially protected groups of butterflies were afterwards shown to exist in tropical Asia, the East Indian Islands and Polynesia by F. Moore (_Proc. Zool. Soc._, 1883, p. 201), and in Africa by E. B. Poulton (_Report Brit. Assoc._, 1897, p. 688). R. Meldola (_Ann. and Mag. Nat. Hist._ x., 1882, p. 417) first pointed out and explained in the same manner the remarkable general uniformity of colour and pattern which runs through so many species of each of the distasteful groups of butterflies; while, still later, Poulton (_Proc. Zool. Soc._, 1887, p. 191) similarly extended the interpretation to the synaposematic resemblances between animals of all kinds in the same country. Thus, for example, longitudinal or circular bands of the same strongly contrasted colours are found in species of many groups with distant affinities.

Certain animals, especially the Crustacea, make use of the special defence and warning colours of other animals. Thus the English hermit-crab, _Pagurus Bernhardus_, commonly carries the sea-anemone, _Sagartia parasitica_, on its shell; while another English species, _Pagurus Prideauxii_, inhabits a shell which is invariably clothed by the flattened _Adamsia palliata_.