Part 7

Some moths have a tape-like proboscis; in others it is cylindrical. It can be made to protrude by gentle pressure on the head, or be unrolled by a pin passed into the centre of the spire; it is composed of innumerable joints, and tapers from the base to the tip. When forcibly unrolled, it often splits lengthwise into halves. At the time of escape from the chrysalis the halves are always free, and they require careful adjustment in order that a continuous sucking-tube may be obtained. A newly emerged moth may be seen to roll and unroll its proboscis repeatedly, until at last the halves cohere in the proper position. Sometimes they begin to dry before the operation is completed, the half-tubes get curled, and then the unfortunate moth becomes incapable of feeding at all. Each half is a demi-canal, whose meeting edges interlock by minute hooks. The mechanism reminds Réaumur of that which connects the barbs of a feather; in both cases the hooks can be adjusted rapidly and completely by stroking from base to tip, and in both a water-tight junction is obtained. Besides the central canal, along which fluids are sucked up, there are lateral canals (tracheæ) filled with air.

Réaumur was careful to correct his anatomical studies by close observation of the live insect. He reared an angle-shades moth, which he kept several days without food. When he saw it repeatedly extending its proboscis, he put near it a piece of sugar. The moth at once began to suck, and became so absorbed in satisfying its hunger that it allowed Réaumur to carry it on a sheet of paper to a window and to examine it closely with a lens. The proboscis was sometimes extended for several minutes at a time, and then rolled up for an instant; its tip was either employed in exploring the surface or closely applied to the sugar. By means of the lens a slender column of liquid was seen to pass along the central canal towards the head. Now and then, however, a limpid fluid was seen to pass down the proboscis; this was the saliva which was used to moisten the sugar, and then sucked up again.

The Budding-out of New Animals (Hydra): another Form of Propagation without Mating (Aphids).

In the year 1744 a young Genevese, Abraham Trembley, tutor in the family of Bentinck, who was then English resident at the Hague, rose into sudden fame by a solid and well-timed contribution to natural history. Trembley and his pupils used to fish for aquatic insects in the ponds belonging to the residence, and in the summer of 1740 he happened to collect some water-weeds, which he put into a glass vessel and set in a window. When the floating objects had come to rest, a small green stalk, barely visible to the naked eye, was found attached to one of the plants. From one end of the stalk filaments or tentacles were seen to project, and these moved slowly about. When the vessel was shaken the stalk and tentacles contracted, but soon extended themselves again. Was this object a plant or an animal? Its shape and colour were those of a plant, and sensitive plants were known which drooped when touched or shaken. Further observation showed that it could move from place to place, which favoured the animal interpretation. Trembley determined to cut the stalk in two; if the halves lived when separated the fact would favour the plant-theory. The halves at first gave no signs of life beyond occasional contraction and expansion, but after eight days small prominences were seen on the cut end of the basal half. Next day the prominences had lengthened; on the eleventh day they seemed to be growing into tentacles. Before long eight fully formed tentacles were visible, and Trembley had two complete specimens in place of one; both were able to move about.

After four years of observation a handsome quarto volume was published, which told the history of "The freshwater Polyp," a name suggested by Réaumur; the Latin name of Hydra was given by Linnæus. Hydra had been discovered and slightly described forty years before by Leeuwenhoek, who had seen two young polyps branching from one parent and spontaneously becoming free. Trembley made out all that a simple lens, guided by a skilful hand and a keen eye, could discover. Thirteen plates were admirably engraved by another amateur, Pierre Lyonet, who was in all respects a fit companion for Trembley. It was proved that Hydra preyed upon living animals, especially upon the Daphnia or water-flea. When it was well nourished it branched spontaneously again and again, forming a compound mass made up of scores or even hundreds of polyps, all connected with a single base. The power of locomotion and the power of devouring prey were held to settle the animal nature of Hydra, a decision to which zoologists have ever since adhered. Lyonet went on to try the effect of division upon some common freshwater worms, and found that each part grew into a complete worm. Artificial division is not indispensable; in the worm called Nais division takes place spontaneously at certain seasons, one segment dividing repeatedly, so as to form the segments of a complete new individual. The process may be repeated until a chain of worms is produced, which at length breaks up.

A nail was thus driven in a sure place. The conception of an animal was enlarged, for it was shown that an animal may branch and multiply in a way hitherto supposed to be peculiar to plants. The old connecting links between animals and plants (zoophytes, sponges, etc.) had never been really investigated; no one knew what sort of organisms formed or inhabited their plant-like skeletons. But Hydra, thanks to Trembley's description, furnished a clear example of an animal which possessed some of the attributes of a plant. Forms more ambiguous than Hydra, such as Volvox and Euglæna, were ultimately to make the distinction between animal and plant very uncertain and shadowy. It was Hydra that gave the first clue to the structure of the zoophytes, and dispelled the false notion that corals are plants, bearing flowers, fruits, and seeds.

By associating with them a number of alien genera.

The third kingdom of nature was taken from the alchemists.

The binomial nomenclature had been gradually coming in ever since the time of the Bauhins.

This discovery is usually attributed to Bonnet, but the testimony of Réaumur (Hist. des Insectes, Vol. VI., p. lvi.) and of Trembley (Hist. des Polypes d'eau douce, p. 323) is decisive in favour of Lyonet.

Baer has remarked that Trembley's discovery appreciably modified the teaching of physiology by showing that an animal without head, nerves, sense-organs, muscles, or blood may perceive, feed, grow, and move about.

At the time when Trembley was demonstrating the asexual propagation of Hydra, Bonnet (supra, p. 45) was demonstrating the asexual propagation of aphids. Both naturalists were natives of Geneva, and both, as well as their associate Lyonet, were in a sense pupils of Réaumur, who not only set them an admirable example, but directed their attention to promising researches and discussed with them the conclusions which might be drawn. Réaumur's experience had seemed to confirm Leeuwenhoek's statement (supra, p. 34) that aphids produce young alive, even though no males are to be found among them; but unlucky accidents defeated his intention to confirm it by experiment, and when Bonnet asked him to suggest a piece of work Réaumur gave him the aphid problem.

Bonnet filled a flower-pot with moist earth, introduced a food-plant together with a single new-born aphid, and covered all up with a bell-jar. In twelve days the aphid produced its first young one; in a month ninety-five had been born from the same unfertilised parent. As many as five generations were obtained without the intervention of a male, each successive parent having been isolated from the moment of its birth. It was, however, discovered, apparently by Lyonet, that though viviparous reproduction without males went on regularly so long as food was plentiful, males appeared towards the end of summer, and fertilised the eggs which were destined to outlast the winter.

The aphids added a new and peculiar example to the known cases of asexual propagation (plants and Hydra). Much discussion followed, but the physiology of that age (and the same is true of the physiology of our own age) was unable to reveal the full significance of the observed facts. Insects have since furnished many instances of unfertilised eggs which yield offspring. One such instance was already recorded, though neither Leeuwenhoek, Réaumur, nor Bonnet knew of it. In the year 1701 Albrecht of Hildesheim placed a pupa in a glass vessel and forgot it. A moth hatched out and laid eggs, from which a number of caterpillars issued.

Lyonet, whom we have more than once had occasion to mention, afterwards became celebrated as the author of one of the most laborious and beautiful of insect-monographs. The structure of the larva of the goat-moth was depicted by him in eighteen quarto plates, crowded with detail.

The Historical or Comparative Method: Montesquieu and Buffon.

About the middle of the eighteenth century we remark the introduction of a new, or almost new, method of investigation, which was destined to achieve great results. Hitherto many men had been sanguine enough to believe that they could think out or decide by argument hard questions respecting the origin of what they saw about them. It was easier, but not really more promising, to resort to ancient books which contained the speculations of past generations of thinkers. Now at last men set themselves to study what is, and by the help of historical facts to discover how it came to be. The new method was first applied to the institutions of human society, but was in the end extended to the earth, life on the earth, and a multitude of other important subjects.

Most writers call this method historical, because history is the chief means by which it seeks to trace causes. Others call it genetic, because it goes back, whenever it can, to origins. It might also be called comparative, because it compares, not only things which are widely separated in time, but also things which are separated in space, things which differ in form or tendency because they have a common origin, and things which differ in origin because they have a common form or tendency. Whether the institutions, arts, and usages of mankind, or the species of plants and animals, are in question, the study of history, together with the comparative study of what now exists, results in increased attention to development, and this again brings to light the continuity of all natural agents and processes—continuity in time and continuity among co-existences. Since the new method has succeeded in tracing the causes of many phenomena which once seemed to obey no law, it has done much to strengthen the belief in universal causation.

Down to the middle of the eighteenth century the book of Genesis had been almost unanimously accepted in Europe as the only source of information concerning the origin of the world, of man, of languages, of arts and sciences. The whole duration of the world was restricted to so brief a space that slow development was impossible, and it was assumed that early history of every kind must be miraculous.

Montesquieu (Esprit des Lois, 1748) was the first to exhibit on an impressive scale the power of the historical method. Natural development, determined by unalterable conditions, was with him the key to the right understanding of the past. It is well known that here and there a great thinker had before Montesquieu framed something like the same conception. The Politics of Aristotle and Vico's study of the historical evolution of the Roman law (1725) are memorable anticipations. By 1748, the date of the Esprit des Lois, or 1749, the date of Buffon's first volumes, which come next before us, Newton's Principia had made students of physics and astronomy practically familiar with the notion of universal causation.

Buffon's place in the history of science is that of one who accomplished great things in spite of weaknesses peculiarly alien to the scientific spirit. It was mainly he who, by strenuous exertions and largely at his own cost, transformed the gardens from which the king's physicians used to procure their drugs into what we now know as the Jardin des Plantes. By the untiring labours of fifty years he produced a Natural History in thirty-six volumes crowded with plates. Having won for himself a place side by side with Montesquieu and Gibbon, he employed it to direct attention to the larger questions of biology and geology. He was a pronounced freethinker, who promulgated bold views with a dexterity which saved him from condemnation by the theological tribunals. When his opinions were declared to be contrary to the teaching of the Church, he printed a conciliatory explanation, but never cancelled the passages objected to, which continued to appear in a succession of editions. His deficiencies, we must admit, were serious. He was a poor observer (partly because of short sight), and had no memory for small details. His enemies were able to taunt him with absurd mistakes, such as that cows shed their horns. He alienated the two foremost naturalists of the eighteenth century, Linnæus and Réaumur, by ignorant and scornful criticisms. His strong propensity to speculation, insufficiently checked by care to verify, might have brought him under the sarcastic remark of Fontenelle, that ignorance is less apparent when it fails to explain what is, than when it undertakes to explain what is not.

Buffon's fame is not seriously impaired by the fact that his great work is no longer read except by those who study the course of scientific thought. Few productions of the human intellect retain their value after a hundred years, and scientific treatises become obsolete sooner than others. It is consoling to recollect that, if their energy is quickly dissipated, it is at least converted into light.

In a history of biology Buffon is naturally a more important figure than Montesquieu. Buffon had imbibed evolutionary views from the Protogæa of Leibnitz, which in turn made use of certain hypotheses of Descartes. The Histoire Naturelle inclines to some theory of evolution, especially in the later volumes. At first Buffon teaches that species are fixed and wholly independent of one another; some years later he is ready to believe that all quadrupeds may be derived from some forty original forms, while in a third and subsequent passage he puts the question whether all vertebrates may not have had a common ancestor. He does not shrink from saying that one general plan of structure pervades the whole animal kingdom—a belief that he could never have adequately supported by facts; Baer long afterwards (1828) searched in vain for evidence on this very point, while Darwin in 1859 admitted that his arguments and facts only proved common descent for each separate phylum of the animal kingdom; he inferred from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form. Elsewhere Buffon makes bold to declare that Nature in her youthful vigour threw off a number of experimental forms of life, some of which were approved and adopted, while others were allowed to survive in order to give mankind a wider conception of her projects. There is generally some gleam of truth in Buffon's most fantastic speculations, but we often wish that he could have attended to the warning of Bossuet: "Le plus grand dérèglement de l'esprit est de croire les choses parce qu'on veut qu'elles soient."

Against all his shortcomings we must set the fact that Buffon strove to interpret the present by the past, the past by the present, geology by astronomy, geographical distribution by the physical history of the continents. One of his maxims expresses the fundamental thought of Lyell's Principles of Geology: "Pour juger de ce qui est arrivé, et même de ce qui arrivera, nous n'avons qu'à examiner ce qui arrive."

Hard-and-fast distinctions are the marks of imperfect theory. Early philosophers distinguished hot and cold, wet and dry, light and dark, male and female, as things different in kind. In later times organic and inorganic, animal and vegetable, the activities of matter and the activities of mind, have been sharply separated. But as knowledge increases these distinctions melt away; it is perceived that the extreme cases are either now connected by insensible gradations, or else spring historically from a common root. Hutton, Lyell, and their successors have made it clear that the history of the earth calls for no agents and no assumptions beyond those that are involved in changes now going on; the present is heir by unbroken descent to the past. Continuity has been established between all forms of energy. Even the chemical elements, once the emblems of independence, give indications that they too had a common origin. The nebular hypothesis, which has been steadily rendered more probable by the scientific discoveries of two centuries, traces all that can be perceived by the senses to a homogeneous vapour, and lays the burden of proof on those who believe that continuity has its limits. Every history, whether of planetary systems, or of the earth's crust, or of human civilisations, religions, and arts, is recognised as a continuous development with progressive differentiation.

Amateur Students of Living Animals.

A history of biology would be incomplete which took no notice of every-day observations of the commonest forms of life. Some of the best are due to the curiosity of men with whom natural history was no more than an occasional recreation. William Turner (a preacher, who became Dean of Wells), Charles Butler (a schoolmaster), Caius and Lister (physicians), Claude Perrault (a physician and architect), Méry and Poupart (surgeons), Frisch (a schoolmaster and philologue), Lyonet (an interpreter and confidential secretary), Roesel (a miniature painter), Henry Baker (a bookseller, who gained a competence by instructing deaf mutes), Leroy (ranger to the King of France), Stephen Hales, Gilbert White and William Kirby (country parsons), and William Spence (a drysalter) were all amateurs in natural history. To this list we might add Willughby, Ray, Leeuwenhoek, Réaumur, De Geer, Buffon, the Hubers, and George Montagu, who were either so fortunate in their worldly circumstances or so devoted to science as to make it their chief, or even their sole pursuit, though they did not look to it for bread. A large proportion of the naturalists whose names have been quoted occupied themselves with the habits and instincts of animals, and biology has been notably enriched by their observations. To Englishmen the most familiar name is that of Gilbert White, in whom were combined thirst for knowledge, exactness in description, and a feeling for the poetry of nature.

White used his influence to encourage what may be called live natural history, which, as he understood it, "abounds in anecdote and circumstance." He bids his correspondents to "learn as much as possible the manners of animals; they are worth a ream of descriptions." His example has done more than his exhortations. He focusses a keen eye upon any new or little-known animal, such as the noctule, the harvest-mouse, or the mole-cricket; detects natural contrivances little, if at all, noticed before, such as the protective resemblance of the stone-curlew's young; dwells upon the practical applications of natural history, such as the action of earthworms in promoting the fertility of soils; and combines facts which a dull man would be careful to put into separate pigeon-holes, such as the different ways in which a squirrel, a field-mouse, and a nuthatch extract the kernels of hazel-nuts.