Wolff was contending against the doctrine of pre-formation in the embryo (see further under the chapter on Embryology), but on account of his acute analysis he should be regarded, perhaps, as the chief forerunner of the founders of the cell-theory. He contended for the same method of development that was afterward emphasized by Schleiden and Schwann. Through the opposition of the illustrious physiologist Haller his work remained unappreciated, and was finally forgotten, until it was revived again in 1812. We can not show that Wolff's researches had any direct influence in leading Schleiden and Schwann to their announcement of the cell-theory. Nevertheless, it stands, intellectually, in the direct line of development of that idea, while the views of Haller upon the construction of organized beings are a side-issue. Haller declared that "the solid parts of animals and vegetables have this fabric in common, that their elements are either fibers or unorganized concrete." This formed the basis of the fiber-theory, which, on account of the great authority of Haller in physiology, occupied in the accumulating writings of anatomists a greater place than the views of Wolff. Bichat, although he is recognized as the founder of histology, made no original observations on the microscopic units of the tissues. He described very minutely the membranes in the bodies of animals, but did not employ the microscope in his investigations. Oken.--In the work of the dreamer Oken (1779-1851), the great representative of the German school of "_Naturphilosophie_," we find, about 1808, a very noteworthy statement to the effect that "animals and plants are throughout nothing else than manifoldly divided or repeated vesicles, as I shall prove anatomically at the proper time." This is apparently a concise statement of the cell-idea prior to Schleiden and Schwann; but we know that it was not founded on observation. Oken, as was his wont, gave rein to his imagination, and, on his part, the idea was entirely theoretical, and amounted to nothing more than a lucky guess. Haller's fiber-theory gave place in the last part of the eighteenth century to the theory that animals and plants are composed of globules and formless material, and this globular theory was in force up to the time of the great generalization of Schleiden and Schwann. It was well expounded by Milne-Edwards in 1823, and now we can recognize that at least some of the globules which he described were the nucleated cells of later writers.