840 MORPHOLOGY thenceforward fully accepted and the Naturphilosophie received its deathblow, while a " second empiric period " of exact anatomical and embryological research seemed for ever to replace it. Such was the popular view ; only a few, like the aged Goethe, whose last literary effort was a masterly critique of the controversy, discerned that the very reverse interpretation was the deeper and essential one, that a veritable " scientific revolution " was in pro gress, and that the supremacy of homological and synthetic over descriptive and analytic studies was thenceforward assured. The irreconcilable feud between the two leaders really involved a reconciliation for their followers ; theories of homological anatomy had thenceforward to be strictly subjected to anatomical and embryological verification, while anatomy and embryology acquired a homological aim. This union of the solid matter and rigorous method of Cuvier with the generalizing spirit and philosophic aims of Geoffrey is well illustrated in the works of Owen ; and, in short, the so-called Cuvierian school is in reality thenceforward also Geoffroyan. The further evolution of the idea of homology is sketched below ( 7), while the extent and rapidity of the subsequent progress of the knowledge of all the structural aspects of plants and animals alike make an historical survey impos sible up to the appearance of the Origin of Species (1859) ; however, no further qualitative advance was possible, since, as Sachs has best pointed out, morphology necessarily contains, under the Linnaean dogma of the constancy of species, the same two inconsistent and irreconcilable lines of thought which we saw represented by Csesalpinus and the early German botanists respectively, on one side the want of strictly scientific classification, and on the other the vaguely-felt existence of a natural relationship. Strict classification of forms supposed constant excludes in fact any natural relationship. The type theory, the theory of unity of organic composition, and the like, are susceptible indeed of two explanations they may be regarded as either ex pressing a creative plan, or taken as purely Platonic and archetypal ideas. Both are tenable on theological and metaphysical grounds respectively, but the fact must not be disguised that of this unity of type no explanation in the least degree scientific, i.e., in terms of the pheno mena of the natural world, does or can exist. The need ful solution was effected by Darwin. The " urpflanze " of Goethe, the types of Cuvier, and the like, at once became intelligible as schematic representations of ancestral organ isms, which, in various and varying environments, have undergone differentiation into the vast multitude of exist ing forms. All the enigmas of structure become resolved ; " representative " and " aberrant," " progressive " and "degraded," "synthetic" and "isolated," "persistent" and " prophetic " types no longer baffle comprehension ; conformity to type represented by differentiated or rudi mentary organs in one organism is no longer contradicted by their entire disappearance in its near allies, while systematist and morphologist become related simply as specialist and generalizer, all through this escape from the Linnsean dogma of the fixity of species. The phenomena of individual development receive interpretation in terms of ancestral history; and embryology thus becomes divided into ontogeny and phylogeny, the latter, too, coming into intimate relation with palaeontology, while classification seeks henceforth the reconstruction of the genealogical tree. All these results were clearly developed in the most important work of the new period, Haeckel s Generelle Morphologic (1866), while the valuable contemporaneous Principles of Biology of Herbert Spencer also gave special attention to the relation of morphology to physiology. 1 1 For bibliography see Carus, Gcschichtc der Zoologie ; Sachs, Ges- 2. Results. Though the preceding is but a meagre outline of the rise and progress of the science, no corre sponding sketch of its results can be here attempted. A description of the refined applications of the doctrine of floral metamorphosis, an inquiry into the morphology of the Cryptogams, or an account of such beautiful homo- logies as those presented by the Arthropods or the Echino- derms is alike impossible ; least of all can we consider the splendid simplification of the supremely complex prob lem of vertebrate structure by the elaboration of a new theory of the skull, and by such luminous discoveries as those of the segmental organs, or of the origin and homo- logies of the spinal and cranial nerves. For these organo- logical conceptions the reader must study such articles as those on AMPHIBIA, BIRDS, HYDKOZOA, MOLLUSCA, &c., and such works as those of Huxley, Gegenbaur and Haeckel, Balfour and Parker, Payer, Eichler, or Asa Gray, and (provided with the needful bibliographical equipment afforded by the various " Jahresberichte " and the kindred English publications) must indeed also plunge into the current literature of the science. And there too must be sought the innumerable attempts at taxonomic synthesis which such organological progress is constantly originating (see ANIMAL KINGDOM, BIOLOGY, vol. iii. p. 690 sq., and VEGETABLE KINGDOM). Embryological generalizations, such as Haeckel s " gastraea theory," Lankester s rival " pla- nula theory," or the ingenious " coelome theory " of Hert- wig, have been recently thoroughly criticized in Balfour s Embryology. The present article will be confined to a brief discussion of a few main problems, commencing with the cell theory and the problem of organic individuality these being selected partly because of their special illus- trativeness and intrinsic importance, partly because they have somewhat less recently been summarized. 3. Histology Cell Theory. Although the application of the simple microscope to the minute structure of plants and animals had been in progress since the end of the 17th century, the rise of modern histology really dates from the Anatomic Generate (1801) of Bichat, which analyses the organism into a series of simple tissues with definite structural characters. This new impulse, together with the improvement of optical appliances, led to much further research. "Fibres" and "globules," "lamina" and " nuclei, " were described, and even "cells" by Mirbel in 1806, and in 1835 Johannes M till or pointed out the existence of cells resembling those of plants in the vertebrate notochord. The cellu lar and nucleated structure of epidermis and other tissues was soon demonstrated, while Robert Brown discovered the nucleus of the vegetable cell. In 1838 Schleiden referred all vegetable tissues to the cellular type, and traced back the plant embryo to a single nucleated cell, while in 1839 Schwann boldly extended this con ception of plant structure and development to the animal world, and so fully constituted the "cell theory." Schwann s cells were essentially nucleated vesicles with fluid contents which originated in an intracellular substance ; but this view was soon abandoned. Dujardin had discovered that the bodies of Foraminifera were composed of a viscous granular contractile sarcodc, and Von Mohl described independently in similar terms the contents of the vegetable cell as protoplasm. This was identi fied by Max Schultze as Dujardin s sarcode, the newer name sur viving ; and this living matter, and not the membrane, he showed to be the essential constituent of the cell, since which his amended definition of the cell as a unit-mass of nucleated protoplasm has been generally accepted. Prevost and Dumas had noticed the segmentation of the ovum into masses as early as 1824, and these were naturally identified as cells immediately after the publication of Schwann s work. In 1846 Kb lliker showed that all tissues arise from these segmentation masses, and that the multiplication of animal and vegetable cells takes place by a continuation of the same process, that of transverse division already observed in the Protozoa. These points gained, the attention of histologists was withdrawn for a considerable time from the scrutiny of the minute structure) of the cell itself to be concentrated on the modes of origin of these unit-masses, and their subsequent differentiation and aggregation into tissues and organs. The minute structure and histogenesis of chichte d. Botanik ; Cuvier, Hist. d. Sci.; Is. G. St-Hilaire, Hist. Nat. Gen.; Masters in M&d.-Chir. Rev., 1858, &c. ; also articles GOETIIK,
LINNAEUS, OKEN, &c.