a small red-and-black butterfly poises statuesque above the purple blossom of this tall field-thistle. with its long sucker it probes industriously floret after floret of the crowded head, and extracts from each its wee drop of buried nectar. as it stands just at present, the dull outer sides of its four wings are alone displayed, so that it does not form a conspicuous mark for passing birds; but when it has drunk up the last drop of honey from the thistle flower, and flits joyously away to seek another purple mass of the same sort, it will open its red-spotted vans in the sunlight, and will then show itself off as one among the prettiest of our native insects. each thistle-head consists of some two hundred separate little bell-shaped blossoms, crowded together for the sake of conspicuousness into a single group, just as the blossoms of the lilac or the syringa are crowded into larger though less dense clusters; and, as each separate floret has a nectary of its own, the bee or butterfly who lights upon the compound flower-group can busy himself for a minute or two in getting at the various drops of honey without the necessity for any further change of position than that of revolving upon his own axis. hence these composite flowers are great favourites with all insects whose suckers are long enough to reach the bottom of their slender tubes.

the butterfly's view of life is doubtless on the whole a cheerful one. yet his existence must be something so nearly mechanical that we probably overrate the amount of enjoyment which he derives from flitting about so airily among the flowers, and passing his days in the unbroken amusement of sucking liquid honey. subjectively viewed, the butterfly is not a high order of insect; his nervous system does not show that provision for comparatively spontaneous thought and action which we find in the more intelligent orders, like the flies, bees, ants, and wasps. his nerves are all frittered away in little separate ganglia distributed among the various segments of his body, instead of being governed by a single great central organ, or brain, whose business it always is to correlate and co-ordinate complex external impressions. this shows that the butterfly's movements are almost all automatic, or simply dependent upon immediate external stimulants: he has not even that small capacity for deliberation and spontaneous initiative which belongs to his relation the bee. the freedom of the will is nothing to him, or extends at best to the amount claimed on behalf of buridan's ass: he can just choose which of two equidistant flowers shall first have the benefit of his attention, and nothing else. whatever view we take on the abstract metaphysical question, it is at least certain that the higher animals can do much more than this. their brain is able to correlate a vast number of external impressions, and to bring them under the influence of endless ideas or experiences, so as finally to evolve conduct which differs very widely with different circumstances and different characters. even though it be true, as determinists believe (and i reckon myself among them), that such conduct is the necessary result of a given character and given circumstances—or, if you will, of a particular set of nervous structures and a particular set of external stimuli—yet we all know that it is capable of varying so indefinitely, owing to the complexity of the structures, as to be practically incalculable. but it is not so with the butterfly. his whole life is cut out for him beforehand; his nervous connections are so simple, and correspond so directly with external stimuli, that we can almost predict with certainty what line of action he will pursue under any given circumstances. he is, as it were, but a piece of half-conscious mechanism, answering immediately to impulses from without, just as the thermometer answers to variations of temperature, and as the telegraphic indicator answers to each making and breaking of the electric current.

in early life the future butterfly emerges from the egg as a caterpillar. at once his many legs begin to move, and the caterpillar moves forward by their motion. but the mechanism which set them moving was the nervous system, with its ganglia working the separate legs of each segment. this movement is probably quite as automatic as the act of sucking in the new-born infant. the caterpillar walks, it knows not why, but simply because it has to walk. when it reaches a fit place for feeding, which differs according to the nature of the particular larva, it feeds automatically. certain special external stimulants of sight, smell, or touch set up the appropriate actions in the mandibles, just as contact of the lips with an external body sets up sucking in the infant. all these movements depend upon what we call instinct—that is to say, organic habits registered in the nervous system of the race. they have arisen by natural selection alone, because those insects which duly performed them survived, and those which did not duly perform them died out. after a considerable span of life spent in feeding and walking about in search of more food, the caterpillar one day found itself compelled by an inner monitor to alter its habits. why, it knew not; but, just as a tired child sinks to sleep, the gorged and full-fed caterpillar sank peacefully into a dormant state. then its tissues melted one by one into a kind of organic pap, and its outer skin hardened into a chrysalis. within that solid case new limbs and organs began to grow by hereditary impulses. at the same time the form of the nervous system altered, to suit the higher and freer life for which the insect was unconsciously preparing itself. fewer and smaller ganglia now appeared in the tail segments (since no legs would any longer be needed there), while more important ones sprang up to govern the motions of the four wings. but it was in the head that the greatest changes took place. there, a rudimentary brain made its appearance, with large optic centres, answering to the far more perfect and important eyes of the future butterfly. for the flying insect will have to steer its way through open space, instead of creeping over leaves and stones; and it will have to suck the honey of flowers, as well as to choose its fitting mate, all of which demands from it higher and keener senses than those of the purblind caterpillar. at length one day the chrysalis bursts asunder, and the insect emerges to view on a summer morning as a full-fledged and beautiful butterfly.

for a minute or two it stands and waits till the air it breathes has filled out its wings, and till the warmth and sunlight have given it strength. for the wings are by origin a part of the breathing apparatus, and they require to be plimmed by the air before the insect can take to flight. then, as it grows more accustomed to its new life, the hereditary impulse causes it to spread its vans abroad, and it flies. soon a flower catches its eye, and the bright mass of colour attracts it irresistibly, as the candle-light attracts the eye of a child a few weeks old. it sets off towards the patch of red or yellow, probably not knowing beforehand that this is the visible symbol of food for it, but merely guided by the blind habit of its race, imprinted with binding force in the very constitution of its body. thus the moths, which fly by night and visit only white flowers whose corollas still shine out in the twilight, are so irresistibly led on by the external stimulus of light from a candle falling upon their eyes that they cannot choose but move their wings rapidly in that direction; and though singed and blinded twice or three times by the flame, must still wheel and eddy into it, till at last they perish in the scorching blaze. their instincts, or, to put it more clearly, their simple nervous mechanism, though admirably adapted to their natural circumstances, cannot be equally adapted to such artificial objects as wax candles. the butterfly in like manner is attracted automatically by the colour of his proper flowers, and settling upon them, sucks up their honey instinctively. but feeding is not now his only object in life: he has to find and pair with a suitable mate. that, indeed, is the great end of his winged existence. here, again, his simple nervous system stands him in good stead. the picture of his kind is, as it were, imprinted on his little brain, and he knows his own mates the moment he sees them, just as intuitively as he knows the flowers upon which he must feed. now we see the reason for the butterfly's large optic centres: they have to guide it in all its movements. in like manner, and by a like mechanism, the female butterfly or moth selects the right spot for laying her eggs, which of course depends entirely upon the nature of the young caterpillars' proper food. each great group of insects has its own habits in this respect, may-flies laying their eggs on the water, many beetles on wood, flies on decaying animal matter, and butterflies mostly on special plants. thus throughout its whole life the butterfly's activity is entirely governed by a rigid law, registered and fixed for ever in the constitution of its ganglia and motor nerves. certain definite objects outside it invariably produce certain definite movements on the insect's part. no doubt it is vaguely conscious of all that it does: no doubt it derives a faint pleasure from due exercise of all its vital functions, and a faint pain when they are injured or thwarted; but on the whole its range of action is narrowed and bounded by its hereditary instincts and their nervous correlatives. it may light on one flower rather than another; it may choose a fresher and brighter mate rather than a battered and dingy one; but its little subjectivity is a mere shadow compared with ours, and it hardly deserves to be considered as more than a semi-conscious automatic machine.