Book - Russian Embryology (1750 - 1850) 13
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Blyakher L. History of embryology in Russia from the middle of the eighteenth to the middle of the nineteenth century (istoryia embriologii v Rossii s serediny XVIII do serediny XIX veka) (1955) Academy of Sciences USSR. Institute of the History of Science and Technology. Translation Smithsonian Institution (1982).
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Publishing House of the Academy of Science USSR Moscow 1955 Translated from Russian Translated and Edited by: Dr. Hosni Ibrahim Youssef # Faculty of Veterinary Medicine Cairo University Dr. Boulos Abdel Malek Head of Veterinary Research Division NAMRU-3, Cairo Arab Republic of Egypt Published for The Smithsonian Institution and the National Science Foundation, Washington, D.C, by The Al Ahram Center for Scientific Translations 1982
The Smithsonian Institution and the National Science Foundation, Washington, D.C by The Al Ahram Center for Scientific Translations (1982)
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Chapter 13. The Discovery of Embryonic Layers - The Dissertation of Kh. I. Pander
While Wolff's investigations represented an epoch in the history of embryology, those works found considerable continuity in the work of the Russian academicians Kh. I. Pander and K. M. Baer. K. A. Timiryazev has emphasized Wolff's significance for the second half of the eighteenth century and Pander's and Baer's for the beginning of the nineteenth century, in his brilliant essay on the history of biology. He wrote that:
Along with the static method of comparison in the first years of the century, Karl Ernst von Baer (and Pander) originated the "formative" method, i.e. the investigation of the organism in its sequence of developmental stages from the ovum. Thereafter the wide study of the history of development began. Here the word "history" was used for the first time, not in that undefined sense as in "natural history," but in the strict sense of specifying the facts in time and not in space. Embryology has grown particularly in zoology, and the most remarkable role has fallen to Russian zoologists (Baer and Pander in the beginning of the century, and Kovalevsky and Mechnikov in the second half) .
Thus, the three stages of embryology are connected with Wolff, then with Pander and Baer, and finally with Kovalevsky and Mechnikov. As Timiryazev pointed out in his familiar work, "The Historical Method in Biology,"
K. A. Timiryazev, "THE MAIN FEATURES OF THE HISTORY OF DEVELOPMENT OF BIOLOGY IN THE 19TH CENTURY," INVESTIGATION, vol. 8 (1939), p. 98.
From the second half of the past century the use of the systematic method of investigation was begun on an organism in successive stages of its embryonic existence; this was later directly called the history of development or embryology. This new science . . . had a special meaning to Russia. Its simultaneous achievements obviously characterize three stages in the fate of Russian science in general. In Petersburg, the brilliant Kaspar Friedrich Wolff, whose courageous and innovative ideas did not find a response among his compatriots, mapped with his brilliant embryological work the route for a new science. Another Russian academician, a student of the famous Dorpat University which was performing such great services to Russian science, Karl Ernst von Baer, was considered the founder of modern embryology. The classical investigations of Baer and his fellow countryman Pander established, with many others, the high standard of science on the Baltic coast. Finally, the names A. Kowalevsky and Mechnikov remain connected with the era of development of that new science A
A well-known role in the preparation of the new period in the history of biology, the period of removing the fantasy of the nature-philosophers, was played by a professor of Wurzburg University, I. Dollinger, who taught Pander and Baer. Both spoke warmly of Dol linger 's influence on their scientific endeavors and of his kind relations with them when they started their work in his laboratory. In his youth Dollinger had been fond of the ideas of Kant and Schelling. Later he sceptically stuck to a priori structures and gave great consideration of the direct empirical study of nature. Pander's and Baer's presence in his laboratory was important, though Dollinger did not himself have a significant effect in science. Baer wrote that the school of Dollinger had done much for the understanding of nature through the investigations of Pander. Baer humbly underestimated himself.
In his autobiography, published on the occasion of the fiftieth anniversary of obtaining his doctoral degree, 3
2. K. A. Timiryazev, "THE HISTORICAL METHOD OF BIOLOGY," INVESTIGATION, vol. 6 (1939), p. 32.
3. Baer, NACHRICHTEN UBER LEBEN UND SCHRIFTEN DES HERRN GEHEIMSRATHS DR. KARL ERNST VON BAER, 1864. St. Petersburg, 1865. 674 pp.
K. M. Baer said how he, in the spring of 1816, had convinced his Dorpat friend Pander to move from Gottingen to l* : iirzburg to work with Dollinger, with whom Baer himself had studied comparative anatomy. Dollinger long cherished a plan to perform a systematic investigation of the chick embryo, but he had neither time nor materials to conclude the work. For this work, a great number of fresh eggs were required. And incubators, because of the lack of thermoregulating facilities, required observation twenty- four hours a day. Further, it was also necessary to invite a graphic artist and an engraver to prepare drawings suitable for reproduction into prints. On a country walk Dollinger, with Baer and Pander, decided that Pander would perform this work and provide the necessary material requirements.
Here it is appropriate to give some biographical information about him, however scanty. Khristian Ivanovich Pander was born on May 12,1794 in Riga to the family of a bank director. In 1812 he entered Dorpat University, and from 1814 he continued studying medicine in Berlin and Gottingen. In 1816 he worked in WUrzburg with Dollinger. After finishing his dissertation in embryology (1817), he worked for about ten years with the artist d 1 Alton in the comparative osteology of contemporary and fossilized animals, and then turned exclusively to paleontological investigations. In 1821 Pander was selected a member of Petersburg Academy of Science; he was from 1822 a scientific senior assistant, and then an academician. In 1827 he resigned because "he did not agree with the internal regulations in the Academy and with the leaders of this organization, "4 After that, Pander became an official of special commissions in the scientific section of the mining department. His responsibilities included processing the paleontologic collection brought into the department, which gave him material for his monograph on paleozoic fish. The work of Pander and his contemporary E.I. Eichwald provided the basis of paleontologic studies in Russia. Having, according to his contemporaries, an extreme modesty and a complete absence of private interest for all science outside his own, Pander remained outside the official world of science. His life was so devoid of scientific honors that even after death he was forgotten. Not one scientific organization kept his obituary or a list of his numerous works .... Many of the results of his scientific investigations were published in the work of others. 5
4. Biography of Pander in MATERIALS FOR THE HISTORY OF SCIENTIFIC AND APPLIED ACTIVITIES IN RUSSIA IN ZOOLOGY AND THE BRANCHES OF SCIENCE RELATED TO IT, PRIMARILY DURING THE LAST THIRTY-FIVE YEARS (1850-1887) , collected by Anatol Bogdanov, Vol. 2 (1889) , p. 55) .
Kristian Ivanovich Pander, Pander died in 1865.
Concerning Pander's working conditions in Wurzburg, Baer reported the following: Dollinger gave Pander the procedures of investigation which he had worked out for early chicken embryos, namely the method of separating the blastoderm from the yolk under water. This method had been previously employed, apparently, by Malpighi and Wolff, but they did not give a description of it. For this reason, it was not known to Haller and Ham, whose achievements therefore were consequently insignificant. Of Ham's work Baer wrote, for example, that "Ham is significantly later than Wolff, even later than Pander. He has offered us investigations of the chick embryo from which it is not possible to know more than that the embryo gets larger and larger. "6 "And thus," Baer continued,
Pander could use Dollinger' s experiments and more expedient methods. But in order to obtain true impressions about this progress (Baer means the most important question in chicken embryology— the formation of the intestines and peritoneal cavity) it is necessary to start from the beginning and follow all the stages of the chick successively. This was done by nobody else but Pander. 7
Already on July 10, 1816 Baer wrote to his friend Dietmar: 8
5. Ibid .
6. Baer, NACHRICHTEN, p. 210.
7. Ibid ., p. 211.
8. Later published in BALTISCHE MONATSSCHRIFT (1893). Cited in R. Stolzle, KARL ERNST VON BAER UND SEINE WELTANSCHAUUNG (Regensburg, 1897), xi + 687 pp. (citation on p. 15) .
Because you have shown such interest in Pander's work, I cannot postpone telling you about it, although Pander does not want that. So look: In all the sciences of nature there is no point more important than the formation of the organism from the original mass; that should hold the key for all physiology and biology. For the lower organisms this formation can be investigated at the emergence of the pouring in animals and water-plants. For the higher animals, only the history of the incubated eggs is available. Although it has been frequently investigated, this has been done partially because of previous ideas, especially the crazy theory of evolution? 9 and partially because attention was directed only towards the development of individual parts, for example in Wolff's work. No engravings have appeared since Malpighi in the seventeenth century, and now Pander has decided to investigate the history of development of the incubated egg and give this work with engravings, perhaps as a dissertation, or as an independent work. In order to get enough eggs, two machines were prepared in which, following Dollinger's recommendations, the eggs are incubated by artificial heating. Paying for a specialist graphic artist and engraver, Pander, by means of these egg shells, stands on the path toward adorning his brow with a laurel wreath. I am proud to be the main stimulus to this action. Be quiet, however, until everything is finished.
Pander worked extremely intensively, and within a year he published his work in Latin, without illustrations, as "Dissertation on the History of the Development of the Incubated Egg throughout the First Five Days. Author Chr. Pander, a Russian from Riga. "10 a German version soon followed, organized along a somewhat different plan and with numerous excellent illustrations, entitled "History of the Development of the Chicken in the Egg."H In the preface to the Latin dissertation Pander warmly referred to DOllinger's kind treatment and to the readiness with which he gave him assistance, and also referred to the friendly conditions and group discussions in the laboratory.
9 . It must be remembered that at the beginning of the nineteenth century, the term evolution was used to mean the development of performed materials (see Chapter 2) .
10. Pander, DISSERTATIO INAUGURALIS SISTENS HISTORIAM METAMORPHOSEUS, QUAM OVUM INCUBATUM PRIORIBUS QUINQUE DIEBUS SUBIT (Wiirzburg, 1817), 69 pp.
11. Pander, BEITRAGE ZUR ENTWICKLUNGSGESCHICHTE DES HUHNCHENS IM EIE (Wurzburg, 1817), 42 pp.
In the introduction, Pander described his method of investi gation. First, he cited the necessity of having available extensive material, since earlier disagreements about chick development originated from the fact that the disputants could not investigate controversial data because of a lack of material. In order to obtain a sufficient number (up to forty) of embryos at one stage, Pander rejected the use of brood hens and instead used an incubating machine of Colman's system, about which Blumenbach had spoken favorably. Pander objected to the current prejudice against incubators, referring to the fact that egg development occurs normally in them and that chickens, as usual, hatch out on the twenty-first day. According to Pander, the temperature in the incubator should not be lower than 28° nor higher than 32°C. A total of more than two thousand developing chicken eggs were used.
The least understood period of chick development was considered to be the earliest. For this reason, Pander limited his investigations to the first five days of incubation. "In this period," Pander wrote, "when the basics of all parts were laid, we did not find anything special that deserves mentioning. "12 Opening the egg, Pander said, should be done in water. To study the early stages (up to the fifth day) , it is necessary to watch for complete separation of the blastoderm from the surrounding parts, because there the processes of embryonic formation actually take place. With this objective, around the cicatrice or, at later stages, along the terminal sinus, Pander cut a segment of the yolk membrane, after which the egg submerged in water separates by itself from the blastoderm. Soon after that, Pander continued, we must begin observing with different types of complex and simple microscopes, with greater or smaller magnification. He recommended placing the observed object on a dark background; then it is comfortable to use the glasses which cover pocket watches. To prepare the blastoderm with instruments, Pander used saucers covered with a layer of wax.
12. Pander, DISSERTATIO, p. 12.
Figure 22. Title page of Pander's Latin dissertation. A copy, belonging to G. I. Fisher, from the library of the Moscow Society of Nature Investigators.
Among his predecessors, Pander spoke first of "Malpighi, who in his 'Epistolary Dissertation on the Formation of the Chicken in the Egg, ' . . . . has given us wonderful presentations accompanied by brief explanations." Pander gave no less consideration to Haller's work, especially to two French memoirs on the development of the heart, and to a Latin paper on this subject. "However, with the greatest praise," Pander discussed Wolff's wonderful observations which are partially stated in the book THE THEORY OF GENERATION, and partially in his treatise "On the Formation of the Intestines" presented in the twelfth and thirteenth volumes of the COMMENTARIES of the St. Petersburg Academy of Science. 13 j n regard to circulation in the vessels and the movement of blood there, Pander referred to Spallanzani' s "Features of Circulation" ("Dei fenomeni della circilogione," 1773) . In concluding his review of the literature, Pander briefly stated: "It is impossible to ignore the careful observations of the most famous master of graphs, Tredern." 14
The first paragraph of Pander's dissertation is devoted to the earliest developmental stages of the incubated egg. On the surface of the yolk and hanging in the egg albumin, Pander saw the small whitish spot, the cicatrice, saying that "Different authors called it by different names (66), but nobody tried to determine how it is situated, where it is located and from where it originates. "15 Pander himself stated that the yolk membrane near this spot is thin and transparent and that egg cicatrices suitable for incubation are distinguished from the formations found in nonfertilized eggs. In the latter the spot is smaller, whiter, granulated, and not completely rounded In fertilized eggs, the spot is larger in size, leaden-whitish and entirely rounded. The surrounding yolk forms an intensively colored zone, and the spot itself is edged with a paler border and has in the center a white spot. On lifting the yolk membrane, Pander found that the spot is composed of one layer of light granules and has the shape of a disk located between the yolk and the yolk membrane. The central part of the disk is attached to the lump underneath, to which the whiter color
13. Ibid . , p. 16.
14. Ibid ., p. 17.
15. Ibid., pp. 18 - 19.
in the center of the spot is related. Thus, Pander distinguished two parts in the cicatrice — the disk, or membranous layer, and the central lump situated below it, to which he gave the name nucleus^ f the cicatrice. Pander gave great consideration to the membranous layer and called it the blastoderm (67) .
At the eighth hour of incubation (§2) C68) the nucleus of the disk is more easily separated from the yolk, but it remains attached to the blastoderm. The latter increases insignificantly in size, its center somewhat clarified.
The twelfth hour of incubation (§ 3) is characterized by further spreading of the blastoderm; its transparent central part also increases and changes the round form into a pear-shaped form. In the blastoderm at that time it is possible to differentiate two regions: the internal region called the transparent area (area pellucida) (69) , surrounded by a non-transparent region, called "the opaque area" (area opaca) . Through the transparent area the nucleus of the cicatrice is visible, "giving Malpighi a reason for his strange mistake and imaginary picture e "17 "The greatest importance," Pander wrote, "is that the blastoderm itself is composed of two layers. This membrane before incubation consists of a single layer of granules. In the process of incubation the second very thin layer appears* however, it is so firm that by prolonged maceration it is possible to separate the blastoderm into two layers." (70) "The internal of these layers," Pander continued, "is connected with the yolk. We will call it later the mucous membrane, and the external homogenous and smooth layer the serous membrane. Both these membranes spread over all the blastoderm and are present in the transparent as well as in the opaque area, with only the difference that in the transparent area the mucous membrane is much more delicate than in the opaque area. "18
16. Called "Pander's nucleus" by subsequent authors,
17. Pander, DISSERT AT 10, p. 25.
18. Ibid., p. 27.
Figure 23. Pander's illustrations from "History of Development of the Chicken in the Eggs."
A (I) Back side: bb — primary folds in their earliest condition; q — fold of the fetal area above the primary folds. B{2) Back side: bb — primary folds; at o they are arch-shaped, joined at the future head end, and, conversely, separated at the tail end. S(3) Back side: bb — primary folds; e — filament of the spinal cord between the primary folds; d — knot- shaped end.
(4) Primary folds closer, especially in the central part of the fetus, where on both sides the first rudiments of the spinal vertebrae are laid; below, where the thin filament of the spinal cord terminates at e in a lancet shape, they again disperse. (5) The peritoneal side: dd — end of the head portion at which the lower edge of the heart is seen (k) ', ef — spinal cord; h — intestinal folds, appearing as lateral borders to the head portion; 11 — lateral borders of the head portion; m — head. £"(6) Fetus from the side of the shell: a — headj b — tail; c — spinal column, seen through the opening of ,he amnion; d — same, under the amnion; e — opening of the amnion. (7) Fetus from the side of the yolk: b — border of the head portion; tail portion; d — intestinal folds; e — spinal cord; ff — arterial stems; g — heart in form of twisted canal.
(8) Fetus in the amnion: a — amnion; b — chorion sac; d — place where all the veins enter the fetus; o — vessels of the chorion; ee — descending veins; m — ascending vein; / — upper arch of the heart; g — lower arch; h — bulb of aorta, from which go out three arch- shaped curved arteries •t, uniting in descending aorta k, Z — left artery with its lateral branch n; o — vein, accompanying this branch. (9) aa — primary folds; go — the cut place (see 10) . K (10) Transverse section (see 9) : aa — primary folds; b — place where the spinal column is situated. (11) aa — primary folds; bbb — head portion; o — its lower border; g — its upper border; fff — borders of the upper membrane of the head portion: dd — cut place (see 12) . M (12) aa — primary folds; b — location of spinal cord; oco — upper layer of the head portion; old intestinal folds. H (13) aa — primary folds; b — place where the spinal cord is formed; oo — folds of the internal layer of the head portion, forming the heart; h — lower border of the head portion; fff — border of the upper layer of the head portion; d — tail portion; -ii, — place of the cut (see 14) . (14) aa — primary folds; b — location of the spinal column; co — folds, forming the heart; co — the vessel layer covering the yolk; f — the upper layer of the head portion. (15)
Longitudinal section made in the amnion of the fetus :
aa — external side of the primary folds; oc — lateral parts of the fetus; ee — serous layer of the blastoderms forming the false amnion; h — opening which later closes; ff — internal layer of these serous layers (especially the amnion) ; g — opening by which the intestines are connected with the yolk; bb — blastoderm. P (16) Transverse section on the lines of (15) . The explanations are the same.
Next Pander referred to the galoons, the white concentric spheres bordering the cicatrice. In a footnote he indicated that until now nobody could explain their structure. Especially Oken, in his "Manual of the Natural History," said that he did not know their nature, and suggested their connection with the vascular system. This suggestion Pander considered devoid of basis. He himself distinguished two types of galoons, one related to the blastoderm, which exists even before the incubation, and another which appears on the second and third day and develops in the yolk itself; the most external of these corresponds with the border of the blastoderm, 9
Until the sixteenth hour of incubation (§ 4) the transparent area has an elongated pear-shaped form. In it are two opaque parallel lines, which in Pander's opinion are the folds forming the blastoderm in the direction of the shell (Drawing 23, 1 - 2) . "These first traces of the developing embryo are called the primary folds, and what is found between them we, with Malpighi, call the intermediate careen," 20 (71).
In one part of the transparent area the primary folds very early turn up to the center and join each other in an arch; and in the opposite area they, on the contrary, become separated. Until this takes place, the transparent area gradually changes its shape from pear-shaped into biscuit-form (Blumenbach) or, Pander suggested, they acquire the shape of sandals. Between the primary folds, Pander saw a quickly developing delicate whitish filament, which he considered the spinal cord. The spinal cord turns into the brain. The opaque area is divided into two zones: the internal repeats the sandal shapes of the transparent area, and the external zone has an elliptical form. The nucleus of the embryonic disk swells, is easily separated from the yolk, and then below it a pit is observed.
19. The term galoon is not employed in later embryological literature, because the rings designated by it are not permanent formations.
20. Pander, DISSERTATIO, pp. 28-30.
In the twentieth hour, embryos (§ 5) are "composed of primary folds and spinal cord, which develop from the blastoderm and in an unknown way are connected with the place of formation," according to Pander. He distinguished two ends — the upper, or the head end, where the folds coincide, and a lower, or tail end, where they are bifurcated. "The cephalic end is somewhat curved inside the egg above the spinal cord and forms in this way a very small half-moon fold." 2 ! Describing in detail the structure and situation of this fold, Pander gets to the characteristics of the conditions of the blastoderm. After dividing it by maceration into two layers, he saw under the microscope that under the internal surface of the serous layer, which is lying on the mucous layer, there is a delicate semitransparent layer of minute granules. This layer is distributed not all over the blastoderm, but occupies only the region of the transparent area and the internal zone of the opaque area, making by itself a division of the opaque area into two zones. Pander especially draws attention to the process of development of this new layer. At about the twelfth hour it is composed of small groups of dispersed granules, forming aggregations in the form of islets; the latter merge in each other but do not form a continuous layer because from them blood islets and blood vessels develop. This layer, the third and middle layer of the blastoderm, Pander called the vascular layer.
In the German version of Pander's work, it is explained distinctly that the blastoderm, which is composed of the embryonic membranes or layers, is considered the origin of the future embryo. All development is nothing other than "like the metamorphosis of the membrane (blastoderm) . . . and its layers. "22
To the end of the first days, according to Pander, the primary rudiments of the vertebrae appear, which in his words are as if hung to the primary folds in the form of nearly quadratic spots of a pale-yellowish color, separated by spaces and situated in two parallel lines. The primary folds at first are straight, then become serpent- shaped, curved and wavy. To the tail the folds disperse, and in the spinal cord they form a convex arch.
21. Ibid . , p. 31.
22. Pander, BEITRXGE ZUR ENTWICKLUNGSGESCHICHTE DES HUHNCHENS IM EIE, p. 6.
The thirtieth hour of incubation (§ 7) is characterized, according to Pander, by the following: "Primary folds previously were opened with the spinal cord situated between them; now they approach each other mainly at the central distance between the head and tail. The edges of the folds move closer; they cover the spinal cord and after that they accrete. When this approach and accretion of the edges occurs along the whole length, the mentioned folds remain apart, and in the head region they keep the serpent -shaped curves and form a number of three or four chambers of larger sizes. "23 The transverse fold becomes a little widened and stretched to the tail end, forming the head portion, as Wolff called it. Pander does not believe that this fold is duplicated, but suggested that the upper one depends on the bending of the embryonic body, and the lower depends on the bending of the blastoderm. At this stage Pander saw the heart rudiment situated under the head as an elongated, not clearly defined sac. The granulated layer, facing from inside to the serous layer, acquires the shape of a net.
Within thirty-six hours after the beginning of incubation (§ 8) the anterior ends of the primary folds get together and accrete with each other, forming the forehead and the facial parts of the embryo. "From each side of this rounded area develops one rounded portion. They are situated a little bit backwards, appearing to be the primary rudiment of the eyes and appear as lateral widenings of the primary central rounded area. "24 The heart, according to Pander, becomes a narrowed, straight, cylindrical canal which extends from the heart depression to the head. The granular layer disintegrates into separate islets; these have a yellowish color, while the granules forming the bordering ring are already stained a red color.
By the forty- second hour of incubation (§9) the end of the head, formerly adjacent to the blastoderm, now is inserted into a small depression formed by the blastoderm, whose fold extends above the head. The fold, forming the border of this depression, represents the rudiment of the amnion. The heart at this stage appeared as an arch curved to the left and divided into three cavities. The head portion now reaches the place of bifurcation of the heart; here also is formed "the heart depression," leading to the esophagus. The lateral borders of the head portion are strongly stretched towards the tail. At the posterior (the lower, according to Pander) end of the fetus appears the wrapped-up part of the blastoderm, which later forms the tail portion, whose borders go along the sides of the embryo and get into the folds near the heart depression. The blood islets at this stage acquire a red color.
23. pander, DISSERTATED, p. 35.
24. Ibid., p. 37.
By the end of the second day (§ 10) the depression, in which the free anterior part of the embryonic body is situated, increases; the head portion, which is outlined by a half-moon border, is distinctly formed. Then the fetus turns to the left side. The granular layer is converted into the vascular plate, which is situated between the two layers of the blastoderm; the latter, therefore, becomes three- layered. The blood islets of the middle layer have now the shape of vessels with their own walls, i.e. they are converted into blood vessels. The spaces, formed by the bent primary folds in the head region become filled with vacuoles and are converted into cavities from which the brain is formed. The posterior (first) space gives the origin to the medulla oblongata, the second to the rounded body of the four hillocks, and the third the narrower part of the brain, while the stems and protuberances of the optic nerve and the most anterior (fourth) is converted into the hemispheres. Pander gave special attention to the fate of the lower space which is adjacent to the yolk surface of the blastoderm. He described two pairs of folds there, the external and internal. The external are formed from all the layers of the blastoderm; and the internal only from the vascular and mucous layers. The external folds, in Pander's opinion, form the peritoneal walls and share in the formation of the intestines. He calls them the peritoneal and intestinal folds. To the internal folds, in correspondence with their subsequent fate, he gave the name of the mesenteric folds. Undoubtedly, these paired folds correspond with those of the embryonic formations which Baer later called the peritoneal and intestinal layers. In this place Pander made a general footnote of several pages devoted to Wolff's investigations and the evolution of Oken's work.
Indicating that Tiedemann, in his manual of zoology, and Meckel, in his translation of Wolff's work, had given credit to Wolff, Pander remarked that Oken instead had attacked Wolff sharply. Oken reproached Wolff for lack of clarity and requested that Tiedemann "follow up completely the development of the intestinal canal, or otherwise there will be a gap ... in Wolff's descriptions. Now we must put an end to all discrepancies. "25 Pander declared also that Oken was not entirely correct in his complaints against Wolff's lack of clarity and in indicating some of his mistakes. "The reason for most of Wolff's mistakes," Pander wrote, "is mainly ... in his assumption that the blastoderm is a single layer . . . and that the origins of the developing changes and their course are connected with it. "26 Pander did not claim to have studied all the layers of the blastoderm completely. He did, however, determine that "these layers, either separated, or connected, are the only origin of the different organs. "27 Pander concluded with a long quotation from Wolff, in which he discussed the formation of the closed intestinal canal from the original bifurcating layers, in order to show his agreement with Wolff.
Pander's observations on the development of the digestive tract revealed the following. The heart depression (Wolff's term, which Pander adopted) forms a wide cavity with a gaping opening. The latter has an oval form; anteriorly it is wider, and posteriorly the intestinal and mesenteric folds, get lost in the posterior part of the tail covers. The colon is formed when the walls of the tail portion move close to each other. Concerning the mesenteric folds, Pander agreed with Wolff that they are the rudiments not only of the mesentery, but also of the kidneys. By the end of the second day the heart bends more and more into the form of a horseshoe, or parabola," developing on the left side.
Chapter 11 of Pander's dissertation is devoted to the incidents of the third day. At that time the blastoderm occupies half of the yolk surface; the form of the transparent area loses its regularity, but in the anterior it remains wider than posteriorly. The blood-carrying system emerges as follows: The net of the previously developing blood vessels is converted into a system of vascular stems and branches, "highly refined decoration of the vascular membranes"; the stems reach the fetus, and the smallest branches reach the peripheral circulation. The arterial stems go out from the fetus in a straight angle, soon divide into three or four branches, while an endless number of small branches fall into the terminal series and also form numerous anastomoses with the thin venous branches. The terminal or peripheral blood circulation, which is called terminal venous circulation, is devoid of vessel walls. From the terminal venous circulation, two or three veins originate, directed to the fetus along its longitudinal axis. The upper descending vein, which is usually duplicated, is a continuation of the terminal sinus; it descends to the head of the fetus, lies on the head portion, and moves close to the heart. The lower ascending vein begins with numerous small branches from the opposite end of the terminal sinus, ascends beside the tail of the embryo, and joins the descending veins near the heart.
25. Ibid . , p. 42 (footnote).
26. Ibid .
27. Ibid.
The heart, which is located on the left side of the fetus and covered with the head portion, is composed of three connected cavities. The first of these cavities is the auricle, the second is the ventricle, and the third is the aortic bulb. The ball-shaped auricle is connected with veins backwards, and anteriorly connected with the continuation of the ventricle. The latter is connected by means of a narrow duct to the widest aortic bulb, from which a narrow cylindrical canal passes into two or three aortic stems. The aorta goes along in a large arch to the heart hole, forming a single trunk which then divides into two, each of which covers a vertebra. By getting narrower, it is lost in the tail region. From these arterial trunks, somewhat further to the middle of the fetus, originate two arteries of the vascular area.^ 8 Blood flow in the vessels begins from the ventricle, where the blood passes along the aorta into two lateral arteries. From their smallest branches it goes partially into the terminal sinus and partially into minute branched veins, and then blood reaches the heart through the descending and ascending veins. Pander described the terminal sinus, and the blood flow in this network.
28. This place in the dissertation is accompanied by an extensive footnote, in which Pander talks about the erroneous description of the embryonic vessels in the works of Tiedemann, Wolff, and especially Oken.
Turning to the digestive tract, Pander remarked that the stomach on the third day is already an elongated form, narrowing anteriorly in the direction of the esophagus. Posteriorly, it has an opening corresponding to the heart depression; the borders of the opening continue posteriorly into the intestinal folds. The mesentery above the stomach, which previously consisted of two layers, now becomes a single layer. The posterior intestine has the form of a cone, with an anterior opening. The body wall, surrounding the cone of the colon, represents the rudiment of the pelvis, which forms by connection with the peritoneal folds. From the pubis, the blastoderm turns to the spinal surface of the fetus. The rudiment of the true amnion is still unclosed above the middle of the back. Along the border of this part, the serous membrane continues in the blastoderm. In a footnote Pander mentioned Tredern's mistake of considering this continuation as the amnion. He noted later that the formation which he called the "false amnion" is not identical with that which Wolff designated by that name. In the posterior part of the embryo, Pander indicated the presence of a lentil-sized cavity which is filled with a transparent fluid; it originates from the surface of the colon and holds the umbilical artery. This cavity, Pander said, is usually called the chorion, and Oken compared it with the mammalian allantois. Pander's observations of development of the liver, lungs and kidneys at this stage correspond with Wolff's descriptions.
Section 12 concerns the embryonic characteristics after four days. The yolk membrane is exhausted and falls behind the blastoderm; the blastoderm surrounds almost all the yolk. Arteries and veins are filled with more intensely colored red blood. In the vascular membrane the arteries are accompanied with the corresponding veins. In the auricle it is possible to see an interceptor in the form of two halfrings, i.e. the beginning of the separation of the left and right auricles. The left is larger than the right and always contains drops of blood seen through its wall. In the ventricle a separation is also observed: above the aortic bulb a reddish oval hillock develops which is situated across the originally existing ventricle. This is the foundation of the right ventricle. From the aortic bulb, closely adjacent to the ventricle, two or three branches go out, and from their base the aorta is formed, which later is bent in the form of an arch. The amnion is only slightly open and includes the whole fetus, which already has rudiments of the legs and wings. The peritoneal folds, which by bending back form the actual amnion, spread along the sides of the fetus, and near the region of the heart and around the borders of the pelvis constitute the borders of the chest and abdominal cavities. The opening of this cavity is the rudiment of the umbilicus.
These observations, which were completely novel, can only suggest that Pander's contemporaries could not understand those features they discovered. Such misunderstandings were displayed not only by Oken, but even by Baer, to whom Pander tried to explain his observations. In his autobiography (p. 212) Baer reports:
Pander had performed his investigations for some months, and I requested that he give me an idea of the method by which the closed body develops from a flat rudiment. Apparently, Pander had at that time a complete, and obviously a correct, idea about that. I remember well that he ran for the assistance of a handkerchief, spread it on his hand, and by bending the fingers tried to give me a visual idea of the formation of the gizzard. But the process remained unclear to me, perhaps because I could not, as I think now, clearly imagine the formation of the intestines.
The subsequent formation of the internal organs Pander described as follows. The stomach is completely closed; it goes into the duodenum to the extent that it is the duodenum rather than the stomach that opens in the regions of the former heart depression. From the duodenum, the middle intestine begins to form. It is at that time composed of two layers, joined at the dorsal borders, which continue into the mesentery. The peritoneal borders of these layers are still separated and extend along the sides into the vascular and mucous layers of the blastoderm. The lungs are located near the heart; they have the shape of extremely delicate semitransparent bodies almost cylindrical in form, terminating in very thin vacuoles. Between the heart and the lungs, below the auricles, the right lobe of the liver is situated, continuing with convex peritoneal and concave dorsal surfaces which are adjacent to the heart; the portal vein goes through this lobe. The left lobe of the liver is narrow; it is located near the stomach and the duodenum. The kidneys are very long, with a lobed structure. They start at the chest region near the lungs and extend along the posterior end of the colon, to which they are connected to the urinary canal. Legs and wings appear as distinct hillocks. On the development of the mandibles, Pander referred to Tredern's observations. The cavity of the chorion as Pander called it, increases in size. In a footnote, Pander mentions the controversy about this organ and refers to Haller's unsuccessful attempts to blow air into the allantois through the intestines, or vice versa. Tiedemann gave more accurate data about the allantois, and Pander quoted him: "This sac is hung on a stem which is rich in vessels including both, the umbilical arteries. The sac is composed of two layers — the external layer which is rich in vessels, and the internal which is thin and without vessels, containing transparent fluid. The cavity of the sac, through a canal extending between the umbilical arteries, connects with the terminal part of the colon or the cloaca .... The external layer of the sac is analogous to the vascular layer (chorion), and the internal layer could correspond to the allantois."
The last paragraph of the dissertation (§ 13) is concerned with the condition of the chick embryo at the fifth day of incubation. The yolk membrane has disappeared. The false amnion, i.e. the serous membrane in Baer's terms, becomes adjacent to the shell membrane. The true amnion is completely closed. The spreading chorion is connected internally with the false amnion. The descending and ascending veins of the vascular area are in the process of disappearing. The middle intestine is almost closed. Between the intestinal layers, there remains only "a small yolk intestinal canal connecting the intestine with the yolk. The serous and mucous layers are entirely separated from each other, the first of which . . . above the back forms the amniotic membrane; the latter together with the mucous layer include the yolk." Pander considered neural development very little. The spinal cord, curved at a straight angle, continues in the medulla oblongata. As a result of the divergence of the lateral parts of the latter, the opened fourth ventricle is formed. The four hillocks are seen in the form of a divided sac. Pander was not sure whether what he had seen was brain material or its membranes. It is difficult to know, he wrote, because "the brain mass even on the sixth day of incubation is still so soft that it flows like tears. "29
At the end of 1817, in Oken's journal I sis, 30 there appeared an extensive review of Pander's dissertation. The review was not signed, but there is reason to believe that it came from Oken himself. The review first of all expressed satisfaction that the publication of these long-awaited investigations was "accomplished with unprecedented diligence, monetary expenditure, and talent." Oken, if indeed he is the author, implied that Pander was not the sole author of his work, but only a participant in a collective with Dollinger and d'Alton. Baer decisively disproved this interpretation. (72)
Oken quite fairly and in detail reviewed the dissertation, alternating statements and extracts with his notes and questions. First he wanted to know what the chalazae are. He expressed the idea that they are tubes through which the food materials pass into the yolk, because, in his opinion, during incubation the albumin and not the yolk diminishes; but it is not directly connected with the embryo. This fantastic assumption is confirmed, in Oken's opinion, by turning the eggs many times. This twists the chalazae, and their assumed pathways close; hence those long-living eggs, i.e. turned many times, do not hatch.
Oken rightly indicated the novelty and importance of the discovery of the embryonic layers. He was only unsatisfied with the description of their development and did not understand how they connect with the yolk membranes. In this respect Oken suggests three possibilities: 1) The layers are mechanically connected with each other, "as drops of wax on paper"; such structures, in his opinion, do not correspond with the nature of living substances, 2) The yolk membrane itself is composed of two layers, and the embryonic membrane separates the internal layer from the external; this suggestion is contrary to the fact of the disappearance of the yolk membrane above the vascular area. 3) The blastoderm is formed from the submerged yolk membrane. This possibility Oken considered the most probable, but it is an entirely arbitrary suggestion, not confirmed by direct observation.
29. Pander, DISSERTATIO, p. 68.
30. ISIS (1817), No. 192, pp. 1529 - 1540.
Oken continued to remark that he did not understand the formation of the two-layered blastoderm, and asked what is present between it and the yolk membrane.
Referring to Pander's description of the formation of the primary folds, Oken considered the most important part of the dissertation to be that on the ptcnatwn saliens.^l He expressed regret only that these parts of the embryo are not illustrated in the schematic ("ideal") drawings. (73) He stated in this respect that "Each prepared anatomical drawings should follow the rule of depicting things not as they look, but as they exist. The so-called drawing from nature is always an expression of what seems to be. The true vision is not that of the artist, but that of the philosopher" (p. 1533) . Concerning the drawings accompanying Pander's German text, Oken said that they allow no understanding of the work because they are not schematic.
A number of details remained unclear to Oken: for example, the topography of the layers or folds in relation to the blastoderm, and the yolk to the shell. To him the method of formation of the spinal cord is not clear; is it a tube or a groove? Oken's perplexity is completely logical for Pander described the gradual closing of the spinal folds, between which from the beginning there is already a threadlike spinal cord. The solution to this confusion was achieved only by Baer, who showed that the thread is not the spinal cord, but a cord where the brain is formed as a result of the closing and accretion of the spinal layers ("primary folds" of Pander) .
31. Punctum sali-ens — a springing point. This is what Aristotle named the rudiment of the heart of the chick embryo, from which, in his opinion, the processes of formation begin. See Aristotle, THE DEVELOPMENT OF ANIMALS, Second Book, 4 (Academy of Science, USSR, 1940) , p. 109.
Concerning Pander's ideas for the period from the twentieth to the thirtieth hour of incubation, Oken accepted the description of blood vessels development and asked only about how the heart develops.
The most perplexing ideas for Oken related to the forty- second hour of incubation. Giving a literal description from Pander concerning the depression in which the head of the embryo is submerged and also concerning the folds forming the borders of this depression and representing the rudiment of the amnion, Oken said "We do not understand that. Also, as with Wolff's description . . . we want to know, can anybody understand that?"
Further on, Oken referred to the following: "The head portion extends to the place of the division of the heart into two stems, and in this region forms the heart depression which leads to the esophagus, the lateral angles of this portion extending forward strongly to the tail." It is not completely clear from the quotation why Oken burst into this tirade: "It is impossible to understand a single letter. All is stated as Wolff stated it, and therefore it is completely unclear. How could the digestive canal be, say, cut off downwards and have the shape of a blowing tube with a gaping empty opening?" Cp. 1535).
Concerning the formation of the rectum from the walls of the tail, Oken again said that this cannot be understood. Then moving from the individual details of the formation of the digestive canal to Pander's general ideas, he wrote: "It cannot all occur like that. The body develops from cavities or sacs, and generally not from layers." Pander and his colleagues, Oken continued, "write as if t^hey completely forget that the yolk and the yolk membrane (which is a cavity or sac) represent an actual part of the body, and that the embryo does not swim in the yolk, as the fish in water."
The source of these comments, freely expressed in a controversial form characteristic of Oken, are the wrongly interpreted observations on the development of mammals, and especially his a priori natural philosophical ideas about the beginning rounded form inherited by all the bodies of nature. 32
Concerning the structure of the blood-carrying vessels of the blastoderm, described by Pander, Oken again stated that they must be looked at as "two cords, whose arteries and veins are connected with each other. Next Oken says that the neighboring vessel is nothing other than the uterus. Aside from these natural philosophical fantasies, Oken suggested a reasonable idea, that the yolk of the chick embryo corresponds to the umbilical sac of the mammalian embryo. Talking about the embryonic vessels he expressed his wish to see a schematic drawing illustrating the connection of the umbilical vessels with the body vessels.
Below (p. 1539), Oken again returned to the question about the development of the intestine, confirming with certainty that he himself had investigated this process and did not understand Wolff's and Pander's descriptions. Having only the drawings for the yet unpublished German text, which were sent to him ahead of time to consider, Oken commented that the "engravings were accomplished so clearly that the figures, it seems, can be judged from the papers" (pp. 1539 - 1540).
Oken's review ends with praise for Pander's unselfish services to science and with Oken's wishes for productive and continuing efforts for the popularization of scientific progress. "We heard," he wrote,
that Pander is going to issue a German edition, not for sale but to offer the nature investigators. This, in any case, is an incomparable offer. It is impossible to neglect the need to serve science, so that such sacrifice, with and without the monstrous expenses which Pander has invested on his own, should be highly appreciated. We can, however, advise printing copies for sale also. There are many friends of science whom Pander may not know and who undoubtedly desire to acquire such work. (p. 1540)
32. More details about that in Chapter 10.
Oken's article was apparently one of the very few responses to Pander's work, aside from K. M. Baer's. (74)
Pander acquainted himself with Oken's review, and his detailed answer soon appeared in I SIS. 33 Oken in turn was interested in Pander's reply; hence in printing it he added his own observations, which he put directly into the text. (75) Expressing his delight for Oken's interest, Pander said that he hurried to answer the questions posed in the review.
Concerning "chalazae," Pander referred to the German text of his work, in which the investigation is given in a different way than in the Latin text, not in regard to the periods of development but in regard to the organ system. There the chalazae are explained as twisted growths of the yolk membrane. The twisting of the chalazae is not a result of frequent turning of the eggs, as Oken thought, because the chalazae are twisted even in eggs that are just laid. There is no cross canal in the chalazae; they do not participate in the suction of the albumen and disappear early, along with the yolk membrane. The albumen, in general, is not used at the beginning of incubation as a food material; its diminution simply depends upon the drying which takes place in the fertilized as well as in the unfertilized egg, as the following data shows. One fertilized egg weighed 805 grains before incubation, and after the lapse of twenty days it lost 131 grains; another unfertilized egg, at the beginning, weighed 785 grains, and within the same period in the incubator lost 121 grains. The loss in weight is observed in eggs kept at room temperature. For two months one of two investigated eggs lost 96.5 grains, and the other lost 63.5 grains. To Oken's unsubstantiated suggestion about the nature of the chalazae, which ascribes to them a. role in feeding the embryo, Pander responded with a simple but convincing experiment.
33. Pander, "Entwickelung des Kuchels," ISIS, v. 3 (1818) , p. 512-524.
Oken's next question concerned the formation of the blastoderm, which Pander addressed by dismissing Oken's error on the genetic connection of the blastoderm and the yolk membrane. "The blastoderm," Pander wrote, "is an entirely isolated part, existing already in the non-incubated egg. It lies on the nucleus and is sharply distinguished from the yolk membrane by its non-transparency and by its loose structure. By lifting the yolk membrane from the yolk it remains lying there. The blastoderm grows hourly under incubation. Later it is composed of three layers — the serous, vascular, and mucous — and finally, after the disappearance of the yolk membrane, it contains the yolk in itself" (p. 514). Oken's response indicated that Pander's clear description had reached his consciousness. "This means that the blastoderm and cover do not have any relationship to the yolk membrane. "34
On Oken's question about the nature and destiny of the nucleus, Pander answered that the nucleus is represented in the form of a whitish cap and corresponds with the cover of the non-incubated egg. At the time of incubation, along with the growth of the blastoderm, it loses its regular form. By the seventh day it gradually disappears.
Oken asked what is situated between the blastoderm and the yolk membrane. Pander's response was: "Nothing; they are directly connected. "35
Concerning the relationship of the primary folds to the spinal cord, which Oken did not understand, Pander was not able to give a satisfactory explanation.
The next two questions, about the development of the heart and the digestive organs, Pander answered together. He noted Oken's mistaken idea about digestive canal formation as a blowing tube with a gaping opening. He objected to the non-empirical nature of Oken's stress on a sac-shaped beginning stage of development. "In order to understand the formation of the heart and the intestinal canal," Pander wrote, "it must be considered that the blastoderm is composed of three layers."
The lower one, membrana pituitosa, takes upon itself the formation of the intestinal canal ; the membrana vasculosa gives rise to the heart and blood vessels; and the membrana serosa is the source of the spinal cord, sides of the body, and amnion. All of this is made clearer by the drawings and descriptions given here. 36 (Figure 24)
34. Pander, "Entwickelung des Kuchels," p. 514.
35. Ibid.
Pander explained the blood system as corresponding to the four stages of its embryonic formation. The first stage, illustrated in Table VIII of the German version, leads to the formation of three blood passages: along the circle at the border of the vascular area (the border vein) , along the branches connecting the border vein with the fetus, and along the vascular stem in the main body of the fetus. The upper or the descending vein (usually double) appears in the form of a stem from the heart-shaped curve of the border vein. The lower or the ascending vein always begins with many branches, passes above the arterial stem and, taking many lateral branches, connects with the upper vein near its entrance in the heart.
The second stage of blood-circulation development is characterized by gradual disappearance of the upper and lower veins. For this, particularly on the fifth day, veins develop and pass along the route of the arteriesj however, the arteries are under the veins. This structure remains to the ninth day, and by the fifteenth day of incubation the vessels of the blastoderm become insignificant and then disappear. The arch of the aorta is formed from two or three branches which go out from the bulb (76) . In the region of the heart depression, this single stem divides into two equal arterial stems, descending in parallel along both sides from the spinal column to the tail. The arteries going out from them at right angle Pander considered vessels corresponding to the iliac arteries of the developing animal. This, of course, is not accurate; this is the umbilical-mesenteric artery. Later all three veins join in the heart, which they enter by a common stem.
36. Ibid., p. 515.
Figure 24. "Ideal cross-section" by Pander
1 - XX - a passage of the yolk membrane in the chalazae, in the nucleus of the cover; "blastoderm of nonincubated ... (a gap in Pander's text) ;
2 - blastoderm of the second day, composed of three layers; CO - the mucous layer; dd. - vascular layer; co - serous layer, f - fetus;
3 - here the layer of the blastoderm is drawn so as to show the change of the serous layer, which at gg has formed the primary folds ;
4 — schematic presentation of the vessels of the layers of
the blastoderm. The serous layer forms a fold on the tail at n and a fold on the head at m , and then together with other membranes it spreads in order to cover the yolk, which they cover more and more. The umbilical ring (Ik) here is still very wide. Parts of the serous membrane I and {, form the amnion, which will later extend through the back of the embryo and close by means of the adhesion of the borders of the folds (77) . The vascular layer, following behind the serous layer, at f forms the heart and the large arteries which are its continuation, and at g (Pander is not sure about this) the sac of the chorion or the allantois. The mucous layer at f forms the food canal, and at g the colon, and between g and f it forms the middle intestine of Wolff (78) ;
5 — A — longitudinal section, c, d, e. designating the same as before; hh — level of the transverse section presented in 5B; v — area in which the heart and food canal develop; w — place of formation of the colon and apparently the chorion; z — spinal cord; G — view from below (from the side of the yolk) the embryo of 5A; aact — area between kk in Fig. A (i.e. the umbilicus) ; bbh — the head portion (gk in Fig. A) ; q- — the tail portion (fk in Fig. A) ; dd — the translucent spinal cord with the primary folds;
6 — A and B — the same as Fig. 5A and 5B; at Ctb the vascular membrane has formed the heart C/ ) ; 2 — spinal cord; X — head depression of the yolk;
7 — A — the same as Fig. 6A; the serous layer begins the formation of the amnion at the head (/) and tail (g) ends; B — i — the posterior end of the umbilicus; g — posterior end of the tail folds of the amnion; h — sac of the chorion;
8 — later fetus; a— heart, transition into the vascular layer dd; bb — intestine, connected by means of the yolk — intestinal duct (which corresponds with the wide previous opening Kk-) with the amnious layer QQ , from which it is formed (79) ; gh — the gradually closing amnion;
9 — still later stage; all the previous designations;
between the intestine and the body of the embryo is the mesentery.
The blood movement takes place, according to Pander, in the following manner. The arterial division of the heart, "with surprising speed and strength" of contracting, sends the blood into the aorta. The push caused by the contraction spreads the blood along the arteries, it then moves to the venous branches and the terminal sinus. From the latter, the blood returns to the heart through the descending and ascending veins.
"The features of blood circulation," Pander wrote,
are so unusually magnificent that we invite everybody who has any desire to investigate nature not to miss the excellent chance given by the incubated egg to try to enjoy this excellent performance .... For this purpose it is recommended to take an egg of three days incubation, to open it in warm water, and to transfer quickly the blastoderm into a glass plate a little submerged in water under a complex microscope with a large optical field, and to observe under dripping warm water which preserves the movement of the blood. 37
At the stage described, Pander thought that there was still no portal vein. Oken responded that if the portal vein is not actually present, then there should be mesenteric vessels, or umbilical arteries; he reasonably asked whether the veins accompanying them are to be considered the mesenteric veins.
The third stage of development of blood circulation begins with the appearance of the chorion sac (h in 7B) in which the umbilical vessels mainly develop. When this organ dies off, the fourth stage of blood circulation begins.
Turning to the development of the amnion, Pander cited his drawings, which yield explanations as "the descriptions of the ideal sections." The explanations are given here in the form of a footnote to Figure 23, with few interpreted observations to interfere.
37. Ibid., p. 520,
To a certain extent, the report of Kazan University Professor E. I. Eichwald (80), "Physiological investigations of the Human Ova, "38 is considered a response to Pander. It was preceded by an extensive introduction in the form of a letter to Pander, in which Eichwald mentioned his studies on embryology ("Observations of the Developing Chicken Egg") performed in Petersburg under Pander's supervision. His interest in embryology led him to the comparative study of the ova of different animals and humans. His work contains few original observations and indicates insufficient acquaintance with the literature, but it has significance in that Eichwald tried to apply a comparative embryological method. He compared parts of the egg, especially the egg membranes39 and provisory organs in different vertebrates (lizards, bony fishes, amphibia, reptiles, birds and mammals, and also in man) , and he even tried to compare the eggs and embryos in vertebrates and invertebrates (insects, Crustacea and worms) . On comparing the structures of eggs or ova of different animals, Eichwald came to the conclusion that "if the yolk in birds is, like that of quadrupeds, amphibia, fish, crabs and insects, composed of numerous balls, then we can presumbably conclude that the human ovum is composed of these same balls" (p. 7). Later Eichwald wrote in detail about the fact that all the layers of the blastoderm and the organs of the embryo developing from them "gradually develop from these primary balls, i.e. all the embryo from the beginning is composed of a granular mass." Thus Eichwald anticipated the cellular structure of the embryo, study of which became widespread in embryology under the later influence of the work of Remak, Reichert, Kolliker, and others.
Pander's embryological investigations had some effect on some of his countrymen working in entomology. Thus, a member of the Moscow Society of Nature Investigators, Gimmerthal, several times reported from Riga about his observations on the metamorphosis of flies (genus Tachina) and butterflies (Naotua ooculatd) .40
38. Eduard Eichwald, "In ovum humanum disquisitio physiologica, Casani," (1824) , ix + 29 pp.
39. Eichwald refers, by the way, to the work of the great Professor L. Bojanus (L. Bojanus, "Uber das Verhaltniss der membrana decidua und reflexa zum Ei des menschlichen Embryo," Vilna, 1820).
Another native of Riga, V. Sodovskii, later published a fairly extensive article about the development of butterflies, with comparative data on the structure of eggs of caterpillars and butterflies and of different scaly-winged insects. In the embryological part of this article Sodovskii discussed especially the process of covering the yolk with the blastoderm, and the development of two embryonic membranes — the amnion and the chorion. 41
Pander's significant contributions begin with his definition of the meaning of the blastoderm. He was the first to define that each of the layers or sheets of the blastoderm (he frequently called them membranes) represent the rudiment of a certain system of organs of the developing chick. Therefore Pander must be considered the establisher of studies about the embryonic membranes. The Latin names which Pander gave the membranes — membrana pituitosa, vasculosa, serosa — remained in embryology for a long time; eventually the terms were replaced by the current nonexpressive Greekterms — endoderm, mesoderm, and ectoderm — which do not allow such easy and clear translation.
Next, Pander discovered the primary folds which constitute the first signs of embryonic formation. In fact, Pander did not succeed in connecting these with the formation of the spinal cord, but his wrong interpretation played its positive role. Pander's observations allowed Baer to give the true interpretation. They were sufficiently accurate to eliminate confusion in the description of features, and only the interpretation happened to be wrong. Baer, on another occasion, sympathetically cited Bacon, who said that a mistake leads to the truth more quickly than to confusion.
40. "Metamorphose des insectes. Observations extraites des lettres de M. Gimmerthal a Riga," BULL. SOC. NAT. Moscow, I (1829), pp. 136-141.
41. W. Sodofsy, "Uber die Metamorphose des Schmetterlings , " ARBEITEN DES NATURFORSCHENDEN VEREINS ZU RIGA,
I (1847) , pp. 61-82.
To Pander belongs the immortal merit of extracting from oblivion Wolff's outstanding investigations. Wolff's report "On the Development of the Intestines" Pander understood more correctly than Meckel had in his German translation. Pander's controversy with Oken on intestinal formation had great significance and affected Baer's later work in this direction. Pander's schematic drawings showing the formation and closing up of the amniotic folds and his work on the vascular system are extremely close to Baer's corresponding results published eleven years later. It deserves astonishment that Baer, in his basic work "On the History of Development of Animals," does not even mention Pander's article in ISIS and its accompanying drawings. Knowing Baer's unusual kindness and his efforts to protect Pander's priority, it has to be assumed that he did not read it. That later on he became acquainted with this work is clear from his reference to the article in his autobiography (p. 302) .
A comparison of the historical significance of Pander and Baer could be expressed in the words of Cuvier, which Baer quoted in his biography of the French naturalist: "I am only a Preparator, said he (Cuvier) in one of his lectures. Preparator is a predecessor to Raphael .... I am collecting material for the future great anatomist, and if this happens I want to be taken by him into his service in order to make for him the preparatory work." Such a Preparator was Pander for the great embryologist Baer. By this, his place in the history of embryology is determined.
Cite this page: Hill, M.A. (2024, April 16) Embryology Book - Russian Embryology (1750 - 1850) 13. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Russian_Embryology_(1750_-_1850)_13
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