Morphology (Gr. morphē, 'form'), the study of organic form and structure, the counterpart of physiology, which is concerned with habit and function. The term was first introduced by Goethe in 1817, and is now generally used to include 'the whole statical aspects of the organic world,' as expressed especially in anatomy, both descriptive and comparative, in histology, which is concerned with more minute structure, in palaeontology or the study of extinct forms, and in so much of embryology as consists of structural investigations at different stages of development. But whether engaged with anatomical or histological, palaeontological or embryological studies, the consistent morphologist always considers animals and plants at rest or dead, and analyses them into their parts; while the physiologist on the other hand studies organisms in action or life, and seeks to discover, at various levels of investigation, the physical and chemical changes associated with their activity. Thus, in short, morphology corresponds to the 'statics,' physiology to the 'dynamics' of the organism (see ANATOMY, BIOLOGY, EMBRYOLOGY, FUNCTION, PHYSIOLOGY). To the purely geometrical study of organic forms, their contour, axes, symmetry, &c.—a highly technical inquiry comparable to crystallography—Haeckel applies the special term promorphology.
The simplest task of the morphologist consists in describing form and structure, and the fulfilment of this with increasing thoroughness has placed taxonomy or classification on a sure basis. But this necessarily involves analysing the organism into its parts—organs, tissues, and cells—a method which led, for instance, to the establishment of the cell-theory (see CELL), and has been associated with a parallel deepening of physiological inquiry (see BIOLOGY). Then follows the work of comparing part with part, in a series of organisms or in the same organism, alike in living and extinct, in adult and young forms. This has led to the detection of fundamental similarities of structure or 'homologies' (see HOMOLOGY)—witness Goethe's reduction of the flowering plant to an axis bearing numerous modified or 'metamorphosed' appendages or leaves (see BOTANY, FLOWER); the comparison of oral and other appendages throughout the series of arthropods (see CRUSTACEA, INSECTS); the discovery of the segmented character of the vertebrate skull and brain; the recognition of the ovum as the common starting-point in the life-history of all organisms, or of the gastrula as a predominant stage in the development of animals; the tracing of the embryonic layers to their derivatives in the adult (see EMBRYOLOGY); and so on throughout the triumphs of comparative anatomy and embryology. Finally, the facts of evolution have given the morphologists warrant for yet wider generalising, in which the results of anatomy and histology, embryology and palaeontology, legitimately alloyed with physiological considerations, are welded together into the principles of differentiation.
See the Introduction to Gegenbaur's Comparative Anatomy (trans. by Jeffrey Bell, 1878); Haeckel, Generelle Morphologie (1866); Hatschek, Lehrbuch der Zoologie; standard text-books of Zoology and Botany, and the histories of these sciences by Carus and Sachs respectively; W. His, Unsere Körperform (1875), and also 'On the Principles of Animal Morphology,' Proc. Roy. Soc. Edin. xv. (1888); Herbert Spencer, Principles of Biology (1864).