CHAPTER V

THE PROGRESS OF MINUTE ANATOMY.

The work of Malpighi, Swammerdam, and Leeuwenhoek stimulated investigations into the structure of minute animals, and researches in that field became a feature of the advance in the next century. Considerable progress was made in the province of minute anatomy before comparative anatomy grew into an independent subject.

The attractiveness of observations upon the life-histories and the structure of insects, as shown particularly in the publications of Malpighi and Swammerdam, made those animals the favorite objects of study. The observers were not long in recognizing that some of the greatest beauties of organic architecture are displayed in the internal structure of insects. The delicate tracery of the organs, their minuteness and perfection are well calculated to awaken surprise. Well might those early anatomists be moved to enthusiasm over their researches. Every excursion into this domain gave only beautiful pictures of a mechanism of exquisite delicacy, and their wonder grew into amazement. Here began a new train of ideas, in the unexpected revelation that within the small compass of the body of an insect was embraced such a complex set of organs; a complete nervous system, fine breathing-tubes, organs of circulation, of digestion, etc., etc.

Lyonet.--The first piece of structural work after Swammerdam's to which we must give attention is that of Lyonet, who produced in the middle of the eighteenth century one of the most noteworthy monographs in the field of minute anatomy. This was a work like that of Malpighi, upon the anatomy of a single form, but it was carried out in much greater detail. The 137 figures on the 18 plates are models of close observation and fine execution of drawings.

[Illustration: Fig. 22.--Lyonet, 1707-1789.]

Lyonet (also written Lyonnet) was a Hollander, born in The Hague in 1707. He was a man of varied talents, a painter, a sculptor, an engraver, and a very gifted linguist. It is said that he was skilled in at least eight languages; and at one time he was the cipher secretary and confidential translator for the United Provinces of Holland. He was educated as a lawyer, but, from interest in the subject, devoted most of his time to engraving objects of natural history. Among his earliest published drawings were the figures for Lesser's _Theology of Insects_ (1742) and for Trembley's famous treatise on _Hydra_ (1744).

His Great Monograph.--Finally Lyonet decided to branch out for himself, and produce a monograph on insect anatomy. After some preliminary work on the sheep-tick, he settled upon the caterpillar of the goat moth, which lives upon the willow-tree. His work, first published in 1750, bore the title _Traité Anatomique de la Chenille qui ronge le bois de Saule_. In exploring the anatomy of the form chosen, he displayed not only patience, but great skill as a dissector, while his superiority as a draughtsman was continually shown in his sketches. He engraved his own figures on copper. The drawings are very remarkable for the amount of detail that they show. He dissected this form with the same thoroughness with which medical men have dissected the human body. The superficial muscles were carefully drawn and were then cut away in order to expose the next underlying layer which, in turn, was sketched and then removed. The amount of detail involved in this work may be in part realized from the circumstance that he distinguished 4,041 separate muscles. His sketches show these muscles accurately drawn, and the principal ones are lettered. When he came to expose the nerves, he followed the minute branches to individual small muscles and sketched them, not in a diagrammatic way, but as accurate drawings from the natural object. The breathing-tubes were followed in the same manner, and the other organs of the body were all dissected and drawn with remarkable thoroughness. Lyonet was not trained in anatomy like Malpighi and Swammerdam, but being a man of unusual patience and manual dexterity, he accomplished notable results. His great quarto volume is, however, merely a description of the figures, and lacks the insight of a trained anatomist. His skill as a dissector is far ahead of his knowledge of anatomy, and he becomes lost in the details of his subject.

Extraordinary Quality of the Drawings.--A few figures will serve to illustrate the character of his work, but the reduced reproductions which follow can not do justice to the copper plates of the original. Fig. 23 gives a view of the external appearance of the caterpillar which was dissected. When the skin was removed from the outside the muscles came into view, as shown in Fig. 24. This is a view from the ventral side of the animal. On the left side the more superficial muscles show, and on the right the next deeper layer.

Fig. 25 shows his dissection of the nerves. In this figure the muscles are indicated in outline, and the distribution of nerves to particular muscles is shown.

[Illustration: Fig. 23.--Larva of the Willow Moth. (From Lyonet's Monograph, 1750.)]

Lyonet's dissection of the head is an extraordinary feat. The entire head is not more than a quarter of an inch in diameter, but in a series of seven dissections he shows all of the internal organs in the head. Fig. 26 shows two sketches exhibiting the nervous ganglia, the air tubes, and muscles of the head in their natural position.

Fig. 27 shows the nervous system of the head, including the extremely fine nervous masses which are designated the sympathetic nervous system.

[Illustration: Fig. 24.

Fig. 24.--Muscles of the Larva of the Willow Moth. (From Lyonet's Monograph.)]

[Illustration: Fig. 25.

Fig. 25.--Central Nervous System and Nerves of the Same.]

The extraordinary character of the drawings in Lyonet's monograph created a sensation. The existence of such complicated structures within the body of an insect was discredited, and, furthermore, some of his critics declared that even if such a fine organization existed, it would be beyond human possibilities to expose the details as shown in his sketches. Accordingly, Lyonet was accused of drawing on his imagination. In order to silence his critics he published in the second edition of his work, in 1752, drawings of his instruments and a description of his methods.

[Illustration: Fig. 26.--Dissection of the Head of the Larva of the Willow Moth.]

Lyonet intended to work out the anatomy of the chrysalis and the adult form of the same animal. In pursuance of this plan, he made many dissections and drawings, but, at the age of sixty, on account of the condition of his eyes, he was obliged to stop all close work, and his project remained unfinished. The sketches which he had accumulated were published later, but they fall far short of those illustrating the _Traité Anatomique_. Lyonet died in 1789, at the age of eighty-one.

[Illustration: Fig. 27.--The Brain and Head Nerves of the Same Animal.]

Roesel, Réaumur, and De Geer on Insect Life.--We must also take note of the fact that, running parallel with this work on the anatomy of insects, observations and publications had gone forward on form, habits, and metamorphosis of insects, that did more to advance the knowledge of insect life than Lyonet's researches. Roesel, in Germany, Réaumur, in France, and De Geer, in Sweden, were all distinguished observers in this line. Their works are voluminous and are well illustrated. Those of Réaumur and De Geer took the current French title of _Mémoires pour servir à l'Histoire des Insectes_. The plates with which the collected publications of each of the three men are provided show many sketches of external form and details of external anatomy, but very few illustrations of internal anatomy occur. The sketches of Roesel in particular are worthy of examination at the present time. Some of his masterly figures in color are fine examples of the art of painting in miniature. The name of Roesel (Fig. 28) is connected also with the earliest observations of protoplasm and with a notable publication on the Batrachians.

Réaumur (Fig. 29), who was distinguished for kindly and amiable personal qualities, was also an important man in his influence upon the progress of science. He was both physician and naturalist; he made experiments upon the physiology of digestion, which aided in the understanding of that process; he invented the thermometer which bears his name, and did other services for the advancement of science.

[Illustration: Fig. 28.--Roesel von Rosenhof, 1705-1759.]

Straus-Dürckheim's Monograph on Insect Anatomy.--Insect anatomy continued to attract a number of observers, but we must go forward into the nineteenth century before we find the subject taking a new direction and merging into its modern phase. The remarkable monograph of Straus-Dürckheim represents the next step in the development of insect anatomy toward the position that it occupies to-day. His aim is clearly indicated in the opening sentence of his preface: "Having been for a long time occupied with the study of articulated animals, I propose to publish a general work upon the comparative anatomy of that branch of the animal kingdom." He was working under the influence of Cuvier, who, some years earlier, had founded the science of comparative anatomy and whom he recognized as his great exemplar. His work is dedicated to Cuvier, and is accompanied by a letter to that great anatomist expressing his thanks for encouragement and assistance.

[Illustration: Fig 29.--Réaumur, 1683-1757.]

Straus-Dürckheim (1790-1865) intended that the general considerations should be the chief feature of his monograph, but they failed in this

## particular because, with the further developments in anatomy, including

embryology and the cell-theory, his general discussions regarding the articulated animals became obsolete. The chief value of his work now lies in what he considered its secondary feature, _viz._, that of the detailed anatomy of the cockchafer, one of the common beetles of Europe. Owing to changed conditions, therefore, it takes rank with the work of Malpighi and Lyonet, as a monograph on a single form. Originally he had intended to publish a series of monographs on the structure of insects typical of the different families, but that upon the cockchafer was the only one completed.

Comparison with the Sketches of Lyonet.--The quality of this work upon the anatomy of the cockchafer was excellent, and in 1824 it was accepted and crowned by the Royal Institute of France. The finely lithographed plates were prepared at the expense of the Institute, and the book was published in 1828 with the following cumbersome title: _Considérations Générales sur l'Anatomie comparée des Animaux Articulés auxquelles on a joint l'Anatomie Descriptive du Melolontha Vulgaris (Hanneton) donnée comme example de l'Organisation des Coléoptères_. The 109 sketches with which the plates are adorned are very beautiful, but one who compares his drawings, figure by figure, with those of Lyonet can not fail to see that those of the latter are more detailed and represent a more careful dissection. One illustration from Straus-Dürckheim will suffice to bring the achievements of the two men into comparison.

Fig. 30 shows his sketch of the anatomy of the central nervous system. He undertakes to show only the main branches of the nerves going to the different segments of the body, while Lyonet brings to view the distribution of the minute terminals to particular muscles. Comparison of other figures--notably that of the dissection of the head--will bring out the same point, _viz._, that Lyonet was more detailed than Straus-Dürckheim in his explorations of the anatomy of insects, and fully as accurate in drawing what he had seen.

Nevertheless, the work of Straus-Dürckheim is conceived in a different spirit, and is the first serious attempt to make insect anatomy broadly comparative.

Comment.--Such researches as those of Swammerdam, Lyonet, and Straus-Dürckheim represent a phase in the progress of the study of nature. Perhaps their chief value lies in the fact that they embody the idea of critical observation. As examples of faithful, accurate observations the researches helped to bring about that close study which is our only means of getting at basal facts. These men were all enlisted in the crusade against superficial observation. This had to have its beginning, and when we witness it in its early stages, before the researches have become illuminated by great ideas, the prodigious effort involved in the detailed researches may seem to be poorly expended labor. Nevertheless, though the writings of these pioneers have become obsolete, their work was of importance in helping to lift observations upon nature to a higher level.

Dufour.--Léon Dufour extended the work of Straus-Dürckheim by publishing, between 1831 and 1834, researches upon the anatomy and physiology of different families of insects. His aim was to found a general science of insect anatomy. That he was unsuccessful in accomplishing this was owing partly to the absence of embryology and histology from his method of study.

Newport.--The thing most needed now was not greater devotion to details and a willingness to work, but a broadening of the horizon of ideas. This arrived in the Englishman Newport, who was remarkable not only for his skill as a dissector, but for his recognition of the importance of embryology in elucidating the problems of structure. His article "Insecta" in Todd's _Cyclopædia of Anatomy and Physiology_, in 1841, and his papers in the _Philosophical Transactions_ of the Royal Society contain this new kind of research. Von Baer had founded embryology by his great work on the development of animals in 1828, before the investigations of Dufour, but it was reserved for Newport to recognize its great importance and to apply it to insect anatomy. He saw clearly that, in order to comprehend his problems, the anatomist must take into account the process of building the body, as well as the completed architecture of the adult. The introduction of this important idea made his achievement a distinct advance beyond that of his predecessors.

[Illustration: Fig. 30.--Nervous System of the Cockchafer. (From Straus-Dürckheim's Monograph, 1828.)]

Leydig.--Just as Newport was publishing his conclusions the cell-theory was established (in 1838-39); and this was destined to furnish the basis for a new advance. The influence of the doctrine that all tissues are composed of similar vital units, called cells, was far-reaching. Investigators began to apply the idea in all directions, and there resulted a new department of anatomy, called histology. The subject of insect histology was an unworked field, but manifestly one of importance. Franz Leydig (for portrait see p. 175) entered the new territory with enthusiasm, and through his extensive investigations all structural studies upon insects assumed a new aspect. In 1864 appeared his _Vom Bau des Thierchen Körpers_, which, together with his special articles, created a new kind of insect anatomy based upon the microscopic study of tissues. The application of this method of investigation is easy to see; just as it is impossible to understand the working of a machine without a knowledge of its construction, so a knowledge of the working units of an organ is necessary to comprehend its action. For illustration, it is perfectly evident that we can not understand what is taking place in an organ for receiving sensory impressions without first understanding its mechanism and the nature of the connections between it and the central part of the nervous system. The sensory organ is on the surface in order more readily to receive impressions from the outside world. The sensory cells are also modifications of surface cells, and, as a preliminary step to understanding their particular office, we must know the line along which they have become modified to fit them to receive stimulation.

Then, if we attempt to follow in the imagination the way by which the surface stimulations reach the central nervous system and affect it, we must investigate all the connections. It thus appears that we must know the intimate structure of an organ in order to understand its physiology. Leydig supplied this kind of information for many organs of insects. In his investigations we see the foundation of that delicate work upon the microscopic structure of insects which is still going forward.

Summary.--In this brief sketch we have seen that the study of insect anatomy, beginning with that of Malpighi and Swammerdam, was lifted to a plane of greater exactitude by Lyonet and Straus-Dürckheim. It was further broadened by the researches of Dufour, and began to take on its modern aspects, first, through the labors of Newport, who introduced embryology as a feature of investigation, and, finally, through Leydig's step in introducing histology. In the combination of the work of these two observers, the subject for the first time reached its proper position.

The studies of minute structure in the seventeenth and eighteenth centuries were by no means confined to insects; investigations were made upon a number of other forms. Trembley, in the time of Lyonet, produced his noteworthy memoirs upon the small fresh-water hydra (_Mémoires pour servir à l'histoire des polypes d'eau douce_, 1744); the illustrations for which, as already stated, were prepared by Lyonet. The structure of snails and other mollusks, of tadpoles, frogs, and other batrachia, was also investigated. We have seen that Swammerdam, in the seventeenth century, had begun observations upon the anatomy of tadpoles, frogs, and snails, and also upon the minute crustacea commonly called water-fleas, which are just large enough to be distinguished by the unaided eye. We should remember also that in the same period the microscopic structure of plants began to be investigated, notably by Grew, Malpighi, and Leeuwenhoek (see