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the science dealing with the study of the structure and development of organs and systems in animals by comparing animals of different taxonomic groups. A comparison of the structure of organs in relation to their functions makes it possible to understand the adaptation of animal organisms as integral systems to the conditions of existence, as well as the origin and evolution of various groups of animals.
Comparative anatomy is divided into organology, architectonics, and evolutionary morphology. Organology studies the evolution of individual organs and systems in different animal groups. Classical comparative anatomy (of vertebrates) is a typical example of organology because it examines the evolution of organization by organ systems from the lancelet to man. Architectonics studies the evolution and structure of integral organisms and elucidates the origin and evolution of animal phyla and classes. A specific constituent of architectonics is promorphology, which is concerned with the evolution of symmetry and the body axes in animals. Evolutionary morphology, the most general aspect of comparative anatomy, investigates the principles and ways in which animal organization changes in the course of evolution.
Historical summary. The foundation of comparative anatomy was laid in the fourth century B.C. by Aristotle, who attributed the development of organs to a striving to reach the final goal of the performance of specific functions (teleological explanation). Until the 18th century only scattered comparative anatomical studies were made and only preliminary factual material was obtained. Scientists who participated in the research included Leonardo da Vinci, A. Vesalius, P. Belon, W. Harvey, F. Redi, and J. Swammerdam. In the 18th century in France L. Daubenton described the anatomy of many birds and mammals and F. Vicq-d’Ayr compared the skeletons of various vertebrates and man. The comparative method of studying anatomical material was widely used during this period by P. Camper in the Netherlands, J. Hunter in Great Britain, J. Blumenbach in Germany, and K. F. Vol’f in Russia.
Comparative anatomy reached a new stage of development in the early 19th century, when G. Cuvier made a detailed study of the structure of many animals. He summarized all that was known at that time on the organization of extant and fossil forms in Leçons d’anatomie comparée (vols. 1–5,1800–05). Using a vast amount of data and relying chiefly on his principle of the correlation of organs, Cuvier substantiated his theory of the existence of four separate animal phyla in Le Règne animal (vols. 1–4, 1817). This theory was basic to zoology for a long time. The French evolutionary morphologist E. Geoffroy Saint-Hilaire also made an important contribution to the development of comparative anatomy. He advanced the idea that all animals have a single structural plan that changes under the influence of the environment and laid the foundation for the study of the homology of parts and organs. He called for research on the correlation of organs not only in adult animals but also in the stages of embryonic development. Further advances in comparative anatomy were achieved by the French biologists P. Latreille, M. Savigny, and H. Milne-Edwards, by the Germans J. Müller, J. Meckel, and C. Carus, by the Russian scientist K. M. Ber (who discovered the law of embryonic similarity), and by the English scientist R. Owen (who systematized some general concepts and standardized the terminology for vertebrate bones).
Comparative anatomy entered a long and fruitful period of development with C. Darwin’s theory (1859). The vast quantity of factual material that had accumulated received a new as well as historical interpretation from the standpoint of Darwinism. Along with embryology and paleontology, comparative anatomy became a major source of support for the theory of evolution. Primarily utilizing the comparative method, comparative anatomy distinguished two types of similarity between organs and body parts—homology and analogy. Homologous structures have a common origin, and analogous structures have similar functions. The German biologist K. Gegenbaur is credited with introducing the evolutionary principle into these fundamental concepts. Homologous organs make it possible to establish the relationship between animals, whereas analogous organs develop independently in unrelated animals. Guided by Darwin’s theory and the concept of homology, the English zoologist T. Huxley studied the skulls of vertebrates and rejected Owen’s idealistic theory that the organization of each phylum incorporates a certain abstract predetermined general structural plan, or archetype (archetype theory).
The study of comparative anatomy was further advanced by the German zoologists F. Müller (1864) and E. Haeckel (1866), who substantiated the theory of recapitulation and the basic biogenetic law, which makes it possible to recognize the organizational characteristics of remote ancestors in the ontogeny of animals.
Progress in comparative anatomy was also associated with the use of the comparative method in research conducted by the Russian biologists A. O. Kovalevskii, E. Metchnikoff, V. V. Zalen-skii, and K. N. Davydov, by the British scientists F. Balfour, W. Parker, E. R. Lankester, and E. Goodrich, by the German scientists C. Gegenbaur, R. Wiedersheim, A. Goette, M. Furbringer, K. Heider, L. Bolk, and A. Remane, and by the Czech zoologist B. Hatschek. Paleontological data were used in the study of comparative anatomy in Russia by V. O. Kovalevskii, A. N. Severtsov, and P. P. Sushkin, in the USA by H. Osborn, W. Gregory, and A. Romer, in Great Britain by J. Watson, and in Sweden by E. Stensió and E. Jahrvik. In the late 19th century the Russian scientists Ia. A. Borzenkov, M. Menzbir, V. M. Shimkevich, and their students contributed to the progress of comparative anatomy from the standpoint of Darwinism.
Comparative anatomy reached a high level of development in the early 20th century. At the same time, the old idealist ideas associated with Geoffroy Saint-Hilaire, Owen, and the natural philosophers were revived, especially in Germany, in the form of typology. The typologists A. Nef (1919), A. Meyer (1926), and V. Liubosh (1931) maintained that the structure of all animals is based on a purely theoretical ideal model, or constructive plan of organization. Progress nevertheless continued in the actual physical study of animals. In the USSR, A. N. Severtsov, I. I. Shmal’-gauzen, V. A. Dogel’, P. P. Ivanov, V. N. Beklemishev, D. M. Fedotov, and N. A. Livanov stressed a Darwinist interpretation of the morphological characteristics of evolution.
The need to reexamine the old comparative anatomical problems and phylogenetic theories intensified by the mid-20th century, after major discoveries were made in systematic zoology, paleontology, genetics, cytology, and biochemistry. These discoveries led to increased comparative anatomical research. Among those who worked in the field of evolutionary morphology were the German zoologists A. Dohrn, N. Kleinenberg, and L. Plate, the Belgian paleontologist L. Dollo, the American scientists E. Cope, H. Osborn, G. Simpson, and B. Rensch, and especially the Russian scientist Severtsov and his students. In the book The Morphological Laws of Evolution (1939), Severtsov examined the various ways in which evolutionary changes occur in organs and in the functions of organs and substantiated theories explaining progressive evolution. According to his morphobio-logical theory, a species thrives because of general morpho-physiological progress, individual and often highly specialized adaptations, embryologic adaptations, and morphophysiological regression (occuring in association with parasitism and a sedentary existence). Severtsov’s theory of phylembryogenesis significantly revised and supplemented the biogenetic law and explained the relationship between ontogeny and phytogeny.
In the USSR, there has been significant progress in the field of comparative anatomy since the 1940’s. Shmal’gauzen developed his morphobiological theory of evolution. Beklemishev redefined architectonics and the promorphology of invertebrates based mainly on an analysis of embryonic development. Livanov explained the evolution of various animal phyla based on their ecology and way of life.
Goals and methods. The modern science of comparative anatomy attempts to provide a historical, or comparative anatomical, explanation of the organization of animals, to explain the origin and evolution of groups of animals, to construct a natural system of the animal kingdom, and to determine the morphological laws of evolution.
Because it is a synthetic science, comparative anatomy uses the data and achievements of anatomy, embryology, and paleontology. Adult organisms are not compared with embryos nor extant animals with those that are extinct. However, the macroscopic structure (anatomy) of an organism is studied along with its microscopic structure (histology, cytology). With the evolutionary approach to the structure and form of animals, the boundaries between morphological disciplines disappear, and together the disciplines constitute the single science of comparative morphology. Phytogeny, animal systematics, and comparative anatomy are particularly closely associated. It is difficult to draw boundaries between them because they have many goals in common. A historical, or comparative anatomical, explanation of the structure of an animal, an organ, or a tissue does not dispense with the need to provide a physiological and ecological interpretation of the. structure, that is, to show how an organism or a given morphological structure adapted to the performance of functions and to environmental conditions. Concerned with these questions are functional morphology (pioneered in Russia by P. F. Lesgaft) and ecological morphology, which are special fields of comparative anatomy.
Research in comparative anatomy in the system of the Academy of Sciences of the USSR is primarily conducted by the A. N. Severtsov Institute of Animal Evolutionary Morphology and Ecology in Moscow, the Institute of Zoology in Leningrad, and university subdepartments of zoology. Outside the USSR, research is conducted in the zoological institutes of universities and, less commonly, in institutes of comparative anatomy. International conferences of comparative anatomists have been held under the auspices of the Permanent Committee of International Zoological Congresses (founded 1889) and symposiums sponsored by zoological societies in various countries. Articles on comparative anatomy are published primarily in zoological periodicals.
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A. V. IVANOV