Popular Science Monthly/Volume 36/November 1889/Old and New Methods in Zoology
|OLD AND NEW METHODS IN ZOÖLOGY.|
By M. H. de LACAZE DUTHIERS.
PERMIT me to begin my address by a reminiscence of the origin of this Association, which has haunted me from the moment when you did me the honor to make me your president. It was in July, 1871, when, as we were leaving the Academy of Sciences, Wurtz, taking me by the arm, in his friendly way, said: "Come to my house tomorrow evening; I wish to talk with a few of my friends concerning a scheme which I should be very glad to see carried out." MM. Delaunay, Claude Bernard, Decaisne, and I met at Wurtz's house in the rue Saint-Guillaume on Tuesday evening, and held what we may call the first meeting of the Association. As the last survivor of the company I can not refrain from recalling that intimate interview at which our Association was born. I can still see Wurtz, with, captivating animation and almost feverish activity, pacing the floor with precipitate steps and picturing to us what he thought our society ought to be—and what it has become. He pointed out the priceless advantage to be derived from these meetings, to be held in all parts of France. "We shall," he said, "seek out modest local students living far from the center to meet us and make known the results of their investigations; we shall draw the most timid of them into the scientific current, and shall thus be able to exalt our beloved country in the eyes of the scientific world." Now, the only witness of that first and modest meeting, I believe that I am the interpreter of the feeling of you all in paying one more tribute to the memory of these our first and illustrious co-laborers.
In addressing you I purpose to inquire what zoölogy was, what it is with some, and what it should be. The science of animals of a hundred years ago and that of to-day resemble each other but little. Comparing them and seeking the cause of the great differences, we recognize a few leading facts which I have selected, and of which I will speak. In the former time, when so many reforms were in preparation, and when excited minds were looking for other objects on which to utilize their activity than our sciences, always calm and independent of revolutions as they ought also to be of politics, natural history held but a small place in men's thoughts. In 1789 Linnæus and Buffon had only recently died, and their names were still radiant with the splendor of their living brilliancy; they dominated as absolute masters, and summarized in themselves all of zoölogy. Yet in their minds and works they resembled each other but little. Linnæus , precise, methodical, a classifier first of all, brought order and clearness into the minutest details of the things of nature, and, as he proposed a concise and easy language, his influence became so preponderant that Haller complained of his tyranny. If the reform of the scientific language which Linnæus worked out imposed itself with such force, it was because it answered to one of the needs of the moment. The simplicity, facility, and especially the opportuneness of his nomenclature were the cause of its great success; and it should be added that its value was so great that we have not yet sensibly departed from the rules on which it was founded.
The opposite of Linnæus, Buffon took pleasure in broadly drawn descriptions and pictures; and, when he treated of general considerations, he animated them with a powerful inspiration. A profound thinker, regarding science from an elevated point of view, he engrosses and subjects us. Who among us does not recollect the enthusiasm with which he has read some of the passages in the "Epochs of Nature"? By his reasoning and in the consequences of the observations which, he interpreted, Buffon sought rather to foresee what should be or ought to be, than to fix what he ascertained. He was thus often in advance of his time, and the elevated considerations to which he gave himself were within the grasp of only a small number. Linnæus, on the contrary, described, simply and clearly, what was. With such qualities these two men would often be far from agreeing; and we might apply to them the distinction, which had not yet been expressed, between the school of facts and the school of reasoning. While Linnæus and Buff on thus summarized in themselves all of zoölogy, although from different points of view, their labors lacked a basis the imperious need of which was universally felt. It was already beginning to be understood that the study of the habits, geographical origin, and external characteristics of animals was not enough. At that moment Cuvier appeared. The reform which he introduced in zoölogy was very important, and his work, on the "Animal Kingdom distributed according to its Organization," produced a momentous impression. His great fame, like that of Linnæus, is due to the fact that the modification he made in zoölogical studies corresponded to a certain want, and was a necessary reform that came at the time when it was most needed. Zoölogists of the classifying kind, who occupy themselves only with the externals of animals, have been compared to librarians who arrange their libraries according to the backs or covers of the books, without regard to what is within them. It was Cuvier's great merit that he saw clearly that to reach a truer knowledge of things we must not only be acquainted with the names and external features, but with the internal characteristics as well. To that end he introduced the anatomical idea into the history of animals. In doing it he rendered the greatest service to zoölogy; and to this, too, must be attributed his great success, which was equaled only by that of Linnæus, and also the great reputation in which French zoölogy shone at the beginning of the century. To-day, even those zoölogists who criticise Cuvier the most, nevertheless follow his precepts. We can not apply the same standards of criticism to his work that we would insist upon in judging a work of to-day. To make an equitable estimate, we should put ourselves back to his time, and take account of the gaps in the knowledge of that period, and of the insufficiency of the means which observers could control. It will soon have been a hundred years since Cuvier's work was performed. In that time a great many discoveries have been made, and many conquests have been achieved to cast a new light on questions which were insoluble then.
Zoölogy remained for a long time at the point to which Cuvier led it; and we have to come to the middle of our century to see new ideas brooding and bringing about great modifications in the direction of studies or in some of the branches of the biological sciences. I purpose to supply only a few examples of them. I recollect that in 1855, when I was a professor at Lille, Mr. Huxley wrote to me that "we in England are all stirred up and much perplexed by the discoveries of M. Boucher de Perthes." The reference is, of course, to the interest that was aroused about the cut flints of Saint-Acheul and the famous jaw-bone of Moulin-Quignon. English men of science and geologists came to Amiens, lively discussions took place, a committee of Frenchmen and foreigners was formed and proceeded to the spot to make official investigations. Some fraud and incredulity were mingled in the affair. A workman confessed to me, for a money consideration and a promise of silence, that he had himself fabricated one of the two specimens which I procured, and that it had not lain long enough in the bed to acquire the patina of the other. The point I desire to emphasize is, that the real thing that was discovered then, especially after the visit of the British investigators, was the books, the researches, and the new ideas of M. Boucher de Perthes, which had till then passed unnoticed. The beginning of the prehistoric studies, which have since attained so considerable development, may be dated from this time. Since the discoveries of Boucher de Perthes at Saint-Acheul, and those of Lartet and Christy in Périgord, a part of the history of man has been completely transformed; and geology, so far as concerns the most modern formations, has been subjected to the salutary influence of the new knowledge. What has become of the superannuated ideas that conceived fossil man impossible? What new problems, full of interest, have been presented since the remains were found in Périgord and other places of animals that no longer live where their bones are lying! How many interesting questions have resulted from the simple discovery of a reindeer-horn in a grotto of Eyzies; and what a long road we have gone over since then! Is it strange that the number of explorers has become great, and that liberal and often magnificent encouragement is given them? It would be ungrateful in this connection not to repeat the acknowledgment of our obligations to one of our members—M. Girard, of Lyon—who has bequeathed to our Association one hundred and seventy-two thousand francs to be applied exclusively to researches in prehistoric anthropology; the proceeds of which your committee is able to use this year for the first time.
The lively emotion produced by the discoveries of M. Boucher de Perthes had begun to subside, and researches were going on everywhere, when Darwin's first studies appeared in 1858 and 1859. These dates must always be memorable in the history of natural science, for they mark an epoch from which zoölogical studies entered upon a new course. The learned world, we might say, revolted when Darwin's book appeared. Then enthusiasm, with all its exaggerations, succeeded the first astonishment; and in a little while, a reaction taking place, innumerable investigations were begun with an activity and a curiosity which the previously received ideas were no longer capable of determining. In the first spasm of enthusiasm the great naturalist's theory was called Darwinism; at a later period, dealing less in details and generalizing more, it was called Transformism.
It must be recognized that whatever measure of confidence we put in transformism, whether we accept it in its whole extent and with all its consequences, exaggerate it, modify it, accept it with amendment, or reject it, no one can doubt that it has provoked a truly extraordinary scientific movement. Both partisans and detractors, in seeking for proofs in support of their opinion, whether demanding its secrets from embryogeny, or digging into the strata of the earth in order to interpret the remains of organized beings which they inclose; all, whatever may have been their method, ideas, opinions, or even hostility, have contributed greatly to the progress of zoölogy. Thus we are far from the period of Linnæus, when the external character was everything; and from the period of Cuvier, when the anatomical idea and the study of the exterior were the only guides of the classifier. Now we investigate the connections of beings by going back from the existing to the primitive forms, or vice versa. We try to explain the varied forms under our eyes by the aid of the laws so happily formulated by Darwin. Evolution is encountered everywhere. Whether one be a transformist or not, he must bow and acknowledge the force of the tremendous bound which the impulse given by Darwin has caused.
There are, however, as Claparède has said, "terrible children" of transformism who are more anxious to make a noise around their name than to discover the truth. We must prudently distinguish from them the conscientious students who seek long, scrupulously, and painfully for precise facts in order to deduce from them consequences that will support their theories. These surely advance science, while the others often compromise it. The one thing to oppose to exaggeration, assumption, and enthusiasm is experiment. It is as mandatory to-day as in the preceding period were the reforms which I have mentioned.
While Darwin had an immense and legitimate success, the ideas of Lamarck, who more than half a century before him taught and published the same views on the mutability of species, were long forgotten. Our illustrious compatriot has been treated rather unjustly and severely. There are whole pages in the works of Lamarck containing the theory of transformation completely developed, to which Darwin has added nothing except to confirm them. The minds of zoölogists were not prepared in his time to receive his ideas, and he had not the happy faculty of hitting upon that clear and precise method of statement that imposes itself and makes itself accepted by all. For a reformer to secure a following, his idea should be defined with dazzling clearness and precision, and achieve mastery by virtue of its seductive force. Darwin's exposition of the universal and constant struggle for existence, ending in the selection and survival of the victor, was so true and clear as to lead all readers into accord with it. Cuvier, they said, could reconstruct the whole of an extinct animal from a single bone. The thought spoke to the imagination of the masses; and when he laid down the principle that in an organism, as in an equation, the known terms may be made to give an unknown one, he commanded the admiration of a whole generation. Linnæus, who at a stroke reached the reform science was aspiring after, to rid itself of nonsense in nomenclature, and who found names to fit the occasion, became the tyrant of natural history. It was not possible for Lamarck to realize a similar success; and a comparison of his arguments with those which Darwin brings in support of the doctrine of changes in the forms of animals, and a reference to the epoch in which he wrote, will show why his ideas had to wait for the revelations of the English naturalist before they could be recovered from oblivion.
In view of the surprising discoveries to which the continuous study of the evolution of the lower animals has led, and of the direction of zoölogy under the influence of transformism into new ways, it is impossible not to recognize that experiment alone fulfills the requirements of the moment. It is only through experiment that the great questions of natural philosophy can be answered; that the discussions raised by clashing convictions, hazardous assertions, so-called philosophical doctrines, and venturesome syntheses too often lacking substantial bases, can be justly appreciated or solidly established.
The citation of a few instances will illustrate this assertion. Every one has noticed the gall-nuts on oak-trees, excrescent tumors produced by parasitical insects—the Cynips—which lay their eggs in the mother plant by the aid of a gimlet-shaped ovipositor. The young insect finds within this swelling all that it needs to support life, and quietly in it reaches complete development; and it can easily be caught as it issues from its prison. Entomologists have catalogued a large number of species and genera belonging to the family. In doing thus, they have followed pure and descriptive zoölogy, as it was in the times of Linnæus and Cuvier. Now, it has been found, after watching the evolution of these parasites, that all the genera and species have to be revised. Thus, for example, we find on the superficial roots of an oak-tree galls of varied colors and sizes, the insects issuing from which are wingless. When the trial is made, they will be found incapable of reproducing the warts they came from; they are, besides, all females. Again, we may see, in the spring, the ends of the limbs of the same oak bearing greenish-red tumors, which naturalists have long called oak-apples. They are also galls from which Cynips issue; these too, like the others, are incapable of reproducing the swellings from which they came; but they have wings, and are both male and female. Here, then, are beings totally different, if we study them separately as they come out from their nests. Now let us follow the experimenter, first observing that the insect of the root has been called Biorhiza, and that of the apple Teras. The Biorhizas escape from the roots on which they are hatched, and raise themselves up slowly and painfully, having no wings, to the ends of the branches of the tree. There they lay unfertilized eggs, and cause, by piercing the twigs, the oak-apples from which the Teras issue. On the other side, the Teras, escaping from their apple, copulate, and the fertilized female descends to deposit her eggs in the roots. The Biorhizas, therefore, are hatched from the eggs of the Teras, and the Teras from the eggs of the Biorhizas. Here, then, are two genera wholly distinct in habits, organization, and external characters, which are nevertheless derived each from the other, and which zoölogically ought to form only one. How could M. Adler have discovered these facts, except by experiment? When we remark that the Cynips are relatively high in the animal scale, we are justified in believing that a very great number of similar surprising facts may yet be found among lower forms.
I can not refrain from relating another life-history which is almost a romance. There is a hard sandstone in Provence, interspersed with friable strata, in which burrowing insects construct their chambers. A kind of bee, the Anthophorus, makes nests there and fills them with honey, on which it leaves its egg to float; then, finally, plasters up its chamber. Instead of Anthophores, entirely different insects come out from these nests—Sitaris, belonging to a group very remote from the bees. Let us see how they manage to substitute themselves for the legitimate proprietor of the nest. In the autumn the impregnated female of the Sitaris deposits her eggs in front of the sealed galleries of the Anthophorus. The young are hatched from these eggs, and lie in front of the closed doors, and thus remain in a mass, mingled with the dust and rubbish of the place, through the winter. In the spring, such of the bees as have reached their term come out from their prison. These earliest insects are all males; but, though precocious in being hatched, they are still tender to the changes of the weather, and remain half frozen and torpid in the dust along with the young of the Sitaris. The time has come for the last to begin to act. They have been called Triongulins by Léon Dufour, from the claws with which they are armed, and by which they attach themselves to the bodies of the Anthophores waiting for the next stage in the conditions that favor their development. With fine weather the female Anthophores come out and carry on their work of burrowing and storing up honey till the time of fecundation arrives. Then the Triongulin changes its quarters from the body of the male to that of the female, where it remains on the watch for the laying of the egg, when it transfers itself to that, and with it enters the honey-chamber. With it it is shut up when the Anthophorus closes the door of the chamber for another season. The Triongulin will not eat the honey, for it is sure death to it by drowning if it touches it. It floats on the egg and feeds upon it; when it has used up its ration, it changes its shape, as well as its habits and taste. It is as eager now for the honey as it was to keep away from it, and grows upon it till it goes through another change and becomes the Sitaris which we observe coming out from the chambers of the Anthophorus. Three years of assiduous studies and investigation were required to obtain this curious life-history. Contrast now the results obtained by Léon Dufour, an entomologist and naturalist of the school of Cuvier, with those which M. Fabre has reached by experiment.
I could also show you examples of an excessive socialism in societies of animals, even passing the limits of what has been conceived for men; comprising individuals whose parts are assigned with the greatest precision, some working to feed the collectivity, eating and digesting for all, others possessing the single function of reproduction of the species; and still others serving as beasts of burden for the rest; and looking a little further, we might occasionally discover idlers at rest while their fellows are working to feed them. Take the lobster which we fish from among the rocks and on the sea-coast. In the earlier part of its life, it swims at large on the surface of the fresh water. Its plump and fleshy body, so sought for as a food, is represented then by a broad and extremely thin plate, so peculiar that the zoölogists of the old schools made it not only a genus, but one of the types of a group very remote from its fellows. What would be the difference between these zoölogists and one who should regard the child and the adult of a savage man seen for the first time on some unknown island as forming two genera? Is it not evident that in the times of Linnæus and Cuvier, when they examined animals at only one moment of their existence, naturalists could not follow the filiation of facts which evolution alone reveals to us? The discovery of the Triongulin and the Biorhiza, made when species were defined only according to characteristics falling under the senses, the surprising transformations of which had not been shown us by their evolution, could not possibly have informed us of the true significance of those beings.
I know very well that the quality of an experimental science which I claim for zoölogy is not accorded to us by all students. Those who withhold this recognition are specialists who judge of our science by what they learned of it when they were pursuing their general studies, and when it consisted chiefly of learning names and registering characteristics. They still think it a science of words and memorizing. But we are happily able to reflect that while they have followed and pushed on the science in which they have become masters, they have concerned themselves but little with the advance of the other branches which they have not cultivated; and their present judgment is based on the condition of the science a half-century ago. I think it can be established without contradiction that there is not a zoölogist of the present day, unless he be over-rash or ambitious to enjoy the discovery of a new species, who will venture to affirm that he is acquainted with any being before he has followed its evolution. To follow the evolution, experiments must be instituted, and that constitutes experimental zoölogy. Because our science is now in a critical condition, it is most positively affirmed by the partisans of the transformist theories that it should modify its methods of investigation, and besides registering species should submit unreservedly to experimental control. Such is the conclusion which we logically reach, and which imposes itself upon us to-day.—Translated and abridged for the Popular Science Monthly from the Revue Scientifique.
- ↑ From the presidential address at the French Association for the Advancement of Science.