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Updated: May 21, 2025
As the heart of all Vertebrates is originally, in the light of phylogeny, only a local enlargement of the middle principal vein, it is in perfect accord with the biogenetic law that its first structure in the embryo is a simple spindle-shaped tube in the ventral wall of the head-gut.
But when we recognise the causal correlation of ontogeny and phylogeny expressed in this law, the wonderful facts of embryology are susceptible of a very simple explanation; they are found to be the necessary mechanical effects of the evolution of the stem, determined by the laws of heredity and adaptation.
Where there is free formation of buds there is little flower and commonly no seed, and the converse is also the case. Viviparous plants are an illustration of substitution of vegetative buds for flower. Phylogeny and taxonomy.
That is, by disconnecting one or more of the activating organs from the brain, the motor mechanism might be saved from its self-destruction. Under this hypothesis, that man in disease, as in health, is the product of his phylogeny as well as of ontogeny, the sphere of the physician's activities takes on new aspects of far-reaching and inspiring significance.
When these Dualistic philosophers are consistent they must assign a moment in the phylogeny of the human soul at which it was first "introduced" into man's vertebrate body. I need not insist on the enormous theoretical difficulties of this idea.
The relation of these groups, partly co-ordinate and partly subordinate, in the general scheme is just the same in both cases; and the evolution follows the same lines in both. When, with the assistance of this tree, we follow the formation of the various languages that have been developed from the common root of the ancient Indo-Germanic tongue, we get a very clear idea of their phylogeny.
This important causal nexus finds its simplest expression in "the fundamental law of organic development," the content and purport of which we have fully considered in the first chapter. According to this biogenetic law, ontogeny is a brief and condensed recapitulation of phylogeny.
PHYLETICALLY. In accordance with the phylum or race; racially. PHYLETIC. Pertaining to a race or clan. PHYLOGENY. The history of the evolution of a species or group; tribal history; ancestral development as opposed to ontogeny or the development of the individual. PHYLUM. A term introduced by Haeckel to designate the great branches of the animal and vegetable kingdoms.
V. In Professor Haeckel's speculations on Phylogeny, or the genealogy of animal forms, there is much that is profoundly interesting, and his suggestions are always supported by sound knowledge and great ingenuity. Whether one agrees or disagrees with him, one feels that he has forced the mind into lines of thought in which it is more profitable to go wrong than to stand still.
Professor Haeckel in his "Generelle Morphologie" and in another works, has recently brought his great knowledge and abilities to bear on what he calls phylogeny, or the lines of descent of all organic beings.
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