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Updated: May 26, 2025
There is another and equally curious branch of our subject; namely, serial homologies, or the comparison of the different parts or organs in the same individual, and not of the same parts or organs in different members of the same class.
By considering the embryological structure of man, the homologies which he presents with the lower animals, the rudiments which he retains, and the reversions to which he is liable, we can partly recall in imagination the former condition of our early progenitors; and can approximately place them in their proper place in the zoological series.
But I have a taste for the homologies, I want to go deeply into the subject of embryology, I want to analyze the protonihilates precipitated from pigeon's milk by the action of the lunar spectrum, shall I not follow my star, shall I not obey my instinct, shall I not give myself to the lofty pursuits of science for its own sake? Certainly you may, if you like.
These homologies have never been made before, so far as the writer is aware, but they seem natural, and suggested by a careful examination and comparison with the above-mentioned mandibulate insects. The spring consists of a pair of three-jointed appendages, with the basal joints soldered together early in embryonic life, while the other two joints are free, forming a fork.
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.
And no investigator of homologies doubts that a considerable number of the bones which form the skull of any osseous fish are distinctly homologous with the cranial bones of man. The occipital, the parietal, and frontal, the bones which surround the internal ear, the vomer, the premaxilla, and the quadrate bones, may be given as examples.
The figures on the vessel shown in plate CLXVII are so arranged that there can be little question of their homologies, and from comparisons it is clear that they should all be regarded as representations of birds. There appears no necessity of discussing figures a and b of the plate in this interpretation.
Theophrastus was not very successful in distinguishing the nature of the primary elements of plants, though he was able to separate root, stem, leaf, stipule, and flower on morphological as well as to a limited extent on physiological grounds. But Theophrastus shows by many examples that he is capable of following out morphological homologies.
But no, I am mistaken; from the beginning of all things the Creator knew, that one day the inquisitive children of men would grope about after analogies and homologies, and that Christian naturalists would busy themselves with thinking out his Creative ideas; at any rate, in order to facilitate the discernment by the former that the opercular peduncle of the Serpulae is homologous with a branchial filament, He allowed it to make a detour in its development, and pass through the form of a barbate branchial filament.
And if such a power can be shown to be necessary in this instance, it may also be legitimately used to explain such serial homologies as those of the centipede's segments and of the joints of the backbone. At the same time it is not, of course, pretended that external conditions do not contribute their own effects in addition.
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