United States or Montenegro ? Vote for the TOP Country of the Week !
The chief evidences of the theory of descent are to be found in homologies, in the correspondences of organs and functions, as revealed by comparative anatomy and physiology, in the recapitulation revealed by embryology, in the structure of parasites, in rudimentary organs and reversions to earlier stages, in the distribution of animals and plants, and in the possibility of still transforming, at least to a slight extent, one species into another, by experimental breeding.
"Certain observations on the embryology of the lower animals are held to afford direct proof of this theory of heredity, but they are too technical to be made clear to ordinary readers.
Expanding his starry bosom and standing astraddle, with the air of one who owned the street, the strange being continued, 'Yes, I am lecturing on astronomy, anthropology, archaeology, palaeontology, embryology, eschatology, and so on in a thunderous roll of theoretical sciences apparently beyond the scope of any single university, let alone any single professor.
As the creator of the sciences of comparative anatomy, systematic zoology, embryology, teratology, botany and physiology, his writings have an eternal interest. They present an extraordinary accumulation of facts relating to the structure and functions of various parts of the body. It is an unceasing wonder how one man, even with a school of devoted students, could have done so much.
Species and groups of species which are called aberrant, and which may fancifully be called living fossils, will aid us in forming a picture of the ancient forms of life. Embryology will often reveal to us the structure, in some degree obscured, of the prototypes of each great class.
Of course, there are certain regions of experiment that must be left to specialists, and a scientist who devoted himself to embryology might justly complain of a man who aired views on the subject without adequate study. But as far as life goes, any thoughtful and intelligent man who has lived and reflected is in a sense a specialist.
In reality Weismann only adduces one strict proof, and even that is only laying special stress on what is well known in comparative embryology; namely, the possibility of “predicting” on the basis of the theory of descent, as Leverrier “predicted” Neptune. For instance, in the lower vertebrates from amphibians upwards there is an os centrale in the skeleton of wrist, but there is none in man.
Up to this there is no definite ground in the embryology of the Ascidiae for bringing them into close relationship with the Vertebrates; the same gastrula is formed in the same way in many other animals of different stems. But we now find an embryonic process that is peculiar to the Vertebrates, and that proves irrefragably the affinity of the Ascidiae to the Vertebrates.
Thus, as it seems to me, the leading facts in embryology, which are second to none in importance, are explained on the principle of variations in the many descendants from some one ancient progenitor, having appeared at a not very early period of life, and having been inherited at a corresponding period.
If we suppose with the majority of men that the soul is an independent entity, which has nothing to do with the body originally, but merely inhabits it for a time, and gives expression to its experiences through the brain just as the pianist does through his instrument, we must assign a point in human embryology at which the soul enters into the brain; and at death again we must assign a moment at which it abandons the body.
Word Of The Day