Zoology, the science of animal life, included along with Botany within the science of Biology. What has been said in the article Biology (q.v.) in regard to the place which the study of organisms occupies among other departments of knowledge, and in regard to the general evolution of the science, is entirely relevant in regard to zoology and need not be repeated here.
Departments of Zoological Study: (a) Morphological.—When we study the forms of animal life, or analyse these into their parts—e.g. organs, tissues, and cells; or arrange similar forms in groups—e.g. species, genus, family, order, and class, we are considering morphological or statical relations, the organism's actual life being left out of account. Anatomy and histology (or minute anatomy), the results of classification or taxonomy, so much of embryology as is occupied with the description of form and structure at successive stages in life-history, and of palaeontology as is concerned with the structure of extinct animals must all be included under morphological zoology. (b) Physiological.—When we study the habits of an animal; or analyse its activity into the functions of its parts—e.g. organs, tissues, and cells; or investigate the chemical changes of the living matter itself; or consider the life of the animal as one of a pair, family, or herd, or in its complex inter-relations with the associated fauna and flora, we are investigating dynamic or physiological relations. What is often popularly called 'natural history,' or, more technically, 'bionomics,' is concerned with the 'higher physiology' of animals, that is to say, with their life as intact individualities and as active parts of the complex systems of things which we call nature. (c) Historical.—When we inquire into the fauna characteristic of successive geological ages and endeavour to trace the history of a class, order, or the like; or when we turn our attention to the development of individual animals, and seek to work out their life-history, we are pursuing studies technically described as palæontological and embryological respectively, but agreeing in this that they are both historical or 'genealogical.' (d) Ætiological.—Finally, when we inquire into the conditions of organic change and progress, and endeavour to interpret either individual development (ontogeny) or racial history (phylogeny), our studies are ætiological. As a matter of fact these departments of zoology, though logically distinct, cannot be satisfactorily pursued apart from one another, and all the greater steps of zoological progress have been made by workers who combined the various inquiries. Of such all-round zoological work the best illustration is Charles Darwin. Ray Lankester distinguishes five branches of zoological study: (1) morphography, the work of the collector and systematist; (2) bionomics, the lore of the farmer, breeder, field-naturalist, &c.; (3) zoo-dynamics, zoo-physics, zoo-chemistry, the pursuit of the learned physician—anatomy and physiology; (4) plasmology, the study of the ultimate corpuscles of living matter; (5) philosophical zoology. This division, which introduces some unnecessary new terms, may be readily harmonised with that to which we adhere and which seems to be justified both by its logical clearness and by its correspondence with the great lines of progress in the past.
History.—The rudiments of zoology must be looked for in the ancient lore of the hunter, the fisherman, the shepherd, and the breeder, and much may also be gathered from researches into the history of words, art, and religious customs, but the science first took definite shape in the mind of Aristotle (384-322 B.C.). He seems to have known over 500 animals, and describes the structure and habits of some of these; he laid the foundations of comparative anatomy and taxonomy, and with remarkable insight discerned not a few important generalisations, such as the homology of organs. But the foundations which Aristotle so firmly laid remained for more than fifteen centuries almost unbuilt on, for Pliny (79 A.D.) was little more than an uncritical collector of current information, and Galen (200 A.D.), who dissected monkeys, was rather a human anatomist than a zoologist. It is true, however, that in various countries, and at various times onwards to the Renaissance, there were restless inquisitive spirits who were neither discouraged by the general lack of interest nor silenced by the frowns of the church. Many of these, however, were wont to cloak their zoological enthusiasm in mystical guise, and it is thus that we must interpret many of the allegorical works of mediæval times. Fact and fiction were strangely jumbled; credulity and superstition ran riot along the paths of science; and the long persistence of the Physiologus (see BESTIARY), with its series of fifty fanciful emblems, is typical of the prevalent mood of the dark ages.
The quickening of civilisation brought about by the Crusades, the discovery of new lands by travellers like Marco Polo and Columbus, the founding of universities and learned societies, the establishment of museums and botanic gardens, the invention of printing, the appearance of Aristotle's works in translation and dilution, and many other practical, emotional, and intellectual, movements gave fresh force to science, as indeed to the whole life of man. Among the results of this scientific renaissance were the labours of the 'Encyclopædists'—such as the Englishman Edward Wotton (1492-1555), who wrote a treatise, De Differentiis Animalium; the Swiss Conrad Gesner (1516-65), author of a Historia Animalium; the Italian Aldrovandi (1522-1605); and John Johnston or Jonstonus (1603-75), a Polish Scot, the author of a dozen Latin folios on natural history. By their industry a large mass of facts was accumulated, but of too many it must be said that their intellectual appetite was greater than their powers of digestion, and the progress of science was in quantity more than in quality. About the middle of the 18th century the best aims of the 'Encyclopædists' were realised in Buffon's Histoire Naturelle (15 vols. 1749-67), a work which in spite of its wide range—for the author took all nature for his province—was full of acute perceptions and useful suggestions.
Instead of following further the chronological development of the science, it will be convenient to notice the great workers in the different departments, although this will necessitate a certain amount of multiple reference, some of the greatest zoologists having done equally important work along several lines.
I. Morphological.—In the hands of John Ray and Carl Linnæus the results of their own industry and the accumulations handed down from the Encyclopædists began to take the form of a definite taxonomy. It is an instructive study, for which there is no space here, to contrast the classification which may be inferred from Aristotle's works, and which persisted down to the time of Wotton and even afterwards, with that of Linnæ's Systema Naturæ (1st ed. 1735; 12th, 1768), in which six classes were recognised—Mammalia, Aves, Amphibia, Pisces, Insecta, and Vermes, and to follow the progress of taxonomy onwards. Lamarck drew the distinction between Vertebrates and Invertebrates with greater firmness than heretofore, and distinguished 'apathetic' animals (Infusoria, Polypi, Radiaria, Tunicata, Vermes), 'sensitive' animals (Insecta, Arachnida, Crustacea, Annelida, Cirripedia, Conchifera, and Mollusca), and 'intelligent' Vertebrata (Fishes, Reptiles, Birds, and Mammals). He was a firm believer in a scala naturæ, a regular series of increasing structural complexity, and though this was illusory he did much towards reducing the chaos in which he found Invertebrate animals. Cuvier, in his Règne Animal (1829), elaborated the idea of four great types or embranchements—Vertebrata, Mollusca, Articulata, and Radiata. This rapidly gave way before more careful anatomical analysis, as may be inferred from the early classifications of R. Leuckart, H. Milne-Edwards, and T. H. Huxley, which in turn were destined to be superseded as embryological and palæontological research came to the aid of anatomy, and as taxonomy began to be profoundly influenced by evolutionary conceptions. As a type of these modern or genealogical classifications we may refer to that of E. Ray Lankester, given in his article 'Zoology' in the Encyclopædia Britannica. See also the detailed classifications in the articles VERTEBRATA, &c. in this work.
Among those who have prosecuted the anatomical analysis of the animal body, revealing those homologies on which a sound comparative anatomy is based, Cuvier stands foremost. Meckel, Johannes Müller, Leuckart, Gegenbaur, and Dolrn among Germans; Milne-Edwards and Lacaze-Duthiers in France; Owen, Huxley, and Ray Lankester in England may be cited as representative of comparative anatomists. The analysis of organs into tissues which Bichât worked out in his Anatomie Générale has been followed out in great detail by zoologists, Leydig's Histologie des Menschen und der Thiere (Frankfurt, 1857) being a conspicuous example. The microscopic study of organisms which had been in progress since the days of Malpighi (1628-94), Swammerdam (1637-80), Hook (1635-1702), and especially Leeuwenhoek (1632-1723), led beyond tissues to the component cells, and in 1838-39 Schwann and Schleiden formulated their Zellenlehre, the elaboration and correction of which has been the chief task of modern comparative histologists (see CELL, EMBRYOLOGY, PROTOPLASM). This ultimate morphological analysis which leads to the study of the living matter itself has been aided by the perfecting of the Microscope (q.v.), and by the elaboration of histological technique—fixing, staining, imbedding, and microtome section-cutting.
II. Physiological.—If we disregard a few pioneers and isolated observations, such as Harvey's discovery of the circulation of the blood, we may associate Albrecht von Haller (1708-77) and John Hunter (1728-93) as the founders of physiology. They began to do for the functions of organs what Cuvier did for structure. Among the many illustrious zoologists who have continued their labours Johannes Müller (1801-58) is prominent, for to his own marvellous industry and to the impulse which he gave to his pupils (including many of the most famous living zoologists of Germany) we may refer much of what we know of comparative physiology—a department which has, however, lagged behind its counterpart in comparative anatomy.
Parallel to the morphological analysis from organ to cell was the gradual deepening of physiological study. Bichât's penetration beneath the functions of organs to the properties of tissues; the physiological study of cells by Schwann, Max Schultze, and many others; the experimental work of Claude Bernard, and his appreciation of the essential similarities of function in plants and animals, lead gradually to the modern study of protoplasmic metabolism (see PROTOPLASM), and to such inquiries as those of Krukenberg on the comparative physiology of animals or those of Metschnikoff on the functions of leucocytes.
III. (a) Embryological.—The study of individual development is the youngest department of zoological study, for although Harvey in 1651 sought to establish the fundamental fact ovum est primum commune omnibus animalibus, and the true conception that organs arose by new formation (epigenesis) and not from the unfolding of some invisible preformation, the efforts of his prophetic genius were in great part futile, and the doctrines of the 'preformationists' persisted. Nor did immediate progress follow even when Wolff in 1759 ably reasserted Harvey's doctrine of epigenesis, for it was not till 1817 that Pander took up embryological work virtually where Wolff had left it. In fact it is from the work of Von Baer (1792-1876) that we must date the foundation of modern embryology, of which one of the most illustrious representatives was the late F. M. Balfour (see EMBRYOLOGY). (b) Paleontological.—Although Leonardo da Vinci, Palissy, and others had discerned the true nature of fossils as remains of ancient life, and Woodward (1665-1722) had begun to collect and understand some of these, we need not hesitate to call Cuvier the founder of paleontology. To the fragmentary remains of the extinct he applied with signal success the principle of the 'correlation of parts,' and he was the first to begin that welding of paleontological and anatomical facts which has yielded such important results. Among continuators of his work have been Owen and Huxley in Britain, Quenstedt and Zittel in Germany, Gaudry in France, Marsh and Cope in America.
IV. Ætiological.—Apart from the philosophical speculations of Greek philosophers, a few ætiological suggestions found in the works of Aristotle, the evolutionary epic of Lucretius, and analogous endeavours towards an ætiology, the first serious interpretation of organic nature is that of Buffon. Buffon (1707-88), Erasmus Darwin (1731-1802), and Lamarck (1744-1829) may be called the three old masters in ætiology, and along with these we must associate Treviranus (1776-1837), Geoffroy St Hilaire, Goethe, and Oken. But the great master of them all was Charles Darwin, fellow-workers with whom have been Alfred Russel Wallace, Herbert Spencer, Ernst Haeckel, and Thomas H. Huxley. Of recent years most of the leading zoologists have contributed to the discussion of the problems of evolution, but the most prominent contributions are those of Weismann (q.v.).
BIBLIOGRAPHY.—L. von Graff, Bibliothek des Professors der Zoologie und vergleichenden Anatomie (Leip. 1891); Zoological Record (Zool. Soc., London) from 1864 onwards—annual; Zoologischer Jahresbericht (Zool. Stat., Naples) from 1879 onwards—annual; Bibliotheca Historico-naturalis (Engelmann), works from 1700 to 1846; Bibliotheca Zoologica (Carus and Engelmann), 1846-61, continued by O. Taschenberg, 1861-80; Zoologischer Anzeiger (fortnightly); Anatomischer Anzeiger (fortnightly); Archiv für Naturgeschichte (yearly from 1836); Journal of Royal Microscopical Society (bi-monthly); Royal Society's Catalogue of Scientific Papers (from 1800); L. Agassiz, Bibliographia Zoologie et Geologie (ed. by Strickland and Jardine, Ray Society, Lond. 1848-54). Special bibliographies in the large monographs.
General History of Zoology.—See articles ANATOMY, BIOLOGY, CELL, EMBRYOLOGY, EVOLUTION, PHYSIOLOGY, PROTOPLASM; J. V. Carus, Geschichte der Zoologie (1872); W. Whewell, History of Inductive Sciences (1840); E. Perrier, La Philosophie Zoologique avant Darwin (1884); E. Haeckel, Natural History of Creation (trans. Lond. 1879); E. Ray Lankester, article 'Zoology,' Encyclopædia Britannica; H. A. Nicholson, Natural History: its Rise and Progress in Britain (1888); E. Krause, Die Allgemeine Weltanschauung (1889).
Monographie Series.—Reports of the Voyage of H. M. S. 'Challenger,' Fauna und Flora des Golfs von Neapel, Catalogues of British Museum—Natural History.
General Works.—Bromn's Klassen und Ordnungen des Thierreichs (1859 et seq.); since re-edited by various authorities, Brehm's Thierleben (3d ed. 10 vols. 1890 et seq.), Leunis, Synopsis des Thierreichs (ed. by Ludwig, Hanover, 1886), W. Hatchett Jackson's edition of Rolleston's Forms of Animal Life (Oxford, 1888).
General Morphology.—Haeckel, Generelle Morphologie (1866); H. Spencer, Principles of Biology (1864-66); Leuckart, Morphologie der wirbellosen Thiere (1848); Carus, Thierische Morphologie (1853); Bromn, Morphol. Studien (1858); W. His, Unsere Körperform (1875)—cf. Proc. Roy. Soc. Edin. (1888); Jaeger, Allgemeine Zoologie (1878); Geddes, 'Morphology,' Ency. Brit.
Comparative Anatomy.—G. Cuvier, Leçons d'Anatomie comparée (5 vols. 1708-1805; 2d ed. 8 vols. 1835-46); J. F. Meckel, System der vergleich. Anat. (6 vols. 1821-33); H. Milne-Edwards, Leçons sur la Physiologie et l'Anatomie comparée (14 vols. 1857-81); F. Leydig, Vom Bau des thierischen Körpers (1864); Lehrbuch der Histologie (1857); C. G. Carus, Lehrbuch der Zootomie (1818; 2d ed. 1834); R. Wagner, Handbuch der vergleich. Anat. (1834; 2d ed. 1843-48, 2d vol. by Frey and Leuckart); Von Siebold and Stannius, Lehrbuch d. vergl. Anat. (1845); C. Bergmann and R. Leuckart, Anat.-physiol. Uebersicht des Thierreichs (1852); O. Schmidt, Handbuch der vergl. Anat. (7th ed. 1876); R. Owen, Comparative Anat. (4th ed. 1871); Huxley, Anatomy of Invertebrates (1877) and Vertebrate Animals (1871); C. Gegenbaur, Grundriss d. vergl. Anat. (1878; trans. by
F. Jeffrey Bell, revised by Ray Lankester, 1878); C. Claus, Grundzüge d. Zoologie (4th ed. 1880-82; French trans. 1884) and Text-book of Zoology (trans. by Sedgwick, 1884-85); R. Wiedersheim, Comparative Anat. of Vertebrata (trans. by W. N. Parker, 1886), and larger work untranslated; A. Lang, Text-book of Comp. Anat. (re-ed. of O. Schmidt's, trans. by H. M. and M. Bernard); B. Hatschek, Lehrbuch d. Zoologie (1888 et seq.).
Comparative Physiology.—Claude Bernard, Phénomènes de la Vie Communne aux Animaux et aux Végétaux (1878); Paul Bert, Leçons sur la Physiologie comparée de la Respiration (1870); Krukenberg, Vergleichend-Physiologische Studien und Vorträge (1881-89); F. Jeffrey Bell, Comparative Anatomy and Physiology (1887); A. B. Griffiths, Comparative Physiology (1891); Halliburton, Physiological Chemistry (1891); Bunge, Physiological and Pathological Chemistry (trans. 1890).
Embryology.—A. Kölliker, Entwicklungsgeschichte (2d ed. 1876); F. M. Balfour, Comparative Embryology (1880-81); M. Foster and F. M. Balfour, Elements of Embryology (2d ed. by Sedgwick and Heape, 1883); A. C. Haddon, Introduction to the Study of Embryology (1887); O. Hertwig, Lehrbuch der Entwicklungsgeschichte (2d ed. 1888; French ed. by Julin); E. Korschelt and K. Heider, Entwicklungsgeschichte der wirbellosen Thiere (1890 et seq.).
Paleontological.—H. A. Nicholson and R. Lydekker, Paleontology (1889); K. A. von Zittel, Paleontologie (1876 et seq.); M. Neumayr, Die Stämme des Thierreichs (vol. i. 1889); A. Gaudry, Les Enchainements du Monde Animal (1888-90).
Geographical Distribution.—A. R. Wallace, Geographical Distribution (1876); A. Heilprin, Geographical and Geological Distribution (1887); W. Marshall in Berghaus' Physikal. Atlas 1887; E. L. Trouessart, La Géographie zoologique (1890).
Books of Travelling Naturalists—e.g. C. Darwin, Voyage of the Beagle (Lond. 1844; new ed. 1890); H. W. Bates, Naturalist on the Amazons (new ed., with Life by E. Clodd, Lond. 1892); T. Belt, Naturalist in Nicaragua (2d ed. 1888); A. R. Wallace, Malaya Archipelago (1869), Tropical Nature (1878), Island Life (1880); Wyville Thomson, The Depths of the Sea (1873), Voyage of the Challenger (1885); H. N. Moseley, Naturalist on the Challenger (1879; new ed. 1892).
Etiological.—Darwin, Origin of Species (1859), &c.; Herbert Spencer, Principles of Biology (1864-66); Haeckel, Generelle Morphologie (1866), &c.; A. R. Wallace, Darwinism (1889), &c.
Practical Manuals.—A. M. Marshall and C. H. Hurst, Practical Zoology (3d ed. 1892); T. J. Parker, Zootomy (1884); C. Vogt and E. Yung, Traité d'Anatomie comparée pratique (1885 et seq.); W. K. Brooks, Invertebrate Zoology (Boston, 1882); T. H. Huxley and H. B. Martin, rev. ed. by G. B. Howes and D. H. Scott, Elementary Instruction in Practical Biology (1888); P. Girod, Manipulation de Zoologie (2 vols. 1879-81); A. Bolles Lee, Microtomist's Vade Mecum (2d ed. 1891).
Atlases.—C. G. and O. Carus, Erläuterungstafeln zur vergleichenden Anatomie (1826-52); R. Wagner, Icones Zootomicæ (1841); O. Schmidt, Handatlas der vergl. Anat. (1852); J. V. Carus, Icones Zootomicæ (1857); F. Leydig, Tafeln zur vergl. Anat. (1864); G. B. Howes, Atlas of Practical Elementary Biology (1885); A. de Vayssièr, Atlas d'Anatomie comparée des Invertébrés (1889); W. R. Smith and J. S. Norwell, Illustrations of Zoology (1889).
General Natural History.—Brehm's Thierleben (3d ed. by Pechuel-Loesche, 10 vols. Leip. and Vien. 1890 et seq.); Cassell's Natural History (ed. by P. Martin Duncan, 6 vols. 1882); Standard or Riverside Natural History (ed. by J. S. Kingsley, 6 vols. 1888).