United States or Dominican Republic ? Vote for the TOP Country of the Week !
"Nevertheless, my studies were by no means unfruitful, since they resulted in a triumphant vindication of my theory, which, contrary to that universally received and more closely allied to the 'exploded' Mendel's Law, ascribed the appearance of such monsters not to any strict physiological process but to a hitherto unclassified law of embryology which I had hoped would one day take its place in science under my name.
Darwin's hypothesis, therefore, subject to the production of proof that physiological species may be produced by selective breeding; just as a physical philosopher may accept the undulatory theory of light, subject to the proof of the existence of the hypothetical ether; or as the chemist adopts the atomic theory, subject to the proof of the existence of atoms; and for exactly the same reasons, namely, that it has an immense amount of prima facie probability: that it is the only means at present within reach of reducing the chaos of observed facts to order; and lastly, that it is the most powerful instrument of investigation which has been presented to naturalists since the invention of the natural system of classification, and the commencement of the systematic study of embryology.
How, then, can we explain these several facts in embryology, namely the very general, but not universal difference in structure between the embryo and the adult; of parts in the same individual embryo, which ultimately become very unlike and serve for diverse purposes, being at this early period of growth alike; of embryos of different species within the same class, generally, but not universally, resembling each other; of the structure of the embryo not being closely related to its conditions of existence, except when the embryo becomes at any period of life active and has to provide for itself; of the embryo apparently having sometimes a higher organisation than the mature animal, into which it is developed.
In the lower animals, and as illustrating the embryology of the marine invertebrates, they were especially valuable.
I had followed all these things and many kindred things by dissection and in embryology I had checked the whole theory of development again in a year's course of palaeontology, and I had taken the dimensions of the whole process, by the scale of the stars, in a course of astronomical physics.
And this oneness that everywhere exists is simply a differentiation of the original single cell. The evolution of the cell mirrors the evolution of the species: the evolution of the individual mirrors the evolution of the race. This law, expressed by Goethe, is the controlling shibboleth in all Haeckel's philosophy. In embryology he has proved it to the satisfaction of the scientific world.
It was almost simultaneously formulated by Carl Semper, of Wurtzburg, and Anton Dohrn, of Naples. The latter advanced this theory originally in favour of the failing degeneration theory, with which I dealt in my work, Aims and Methods of Modern Embryology.
We shall begin with the familiar frog which every one knows is a product of a tadpole; passing on to the chick we will learn more facts that will enable us to formulate the main principle of comparative embryology in definite terms; we will then be prepared to extend our survey so as to include somewhat less familiar facts and animals that are even more significant than the first illustrations.
Place side by side all possible genealogical trees of the animal kingdom, whether founded on comparative anatomy, embryology, palæontology, or all combined. They will all disclose this sequence of functions arranged in the same order. Let me call your attention to the fact that this order is not due to chance, but rests upon a physiological basis.
Its anterior portion appears from embryology to be very primitive. 3. The small brain, or cerebellum, which in all higher forms is the centre for co-ordination of the motions of the body. 4. The medulla, which controls especially the internal organs.
Word Of The Day