Intermembral homologies : the correspondence of the anterior and posterior limbs of vertebrates / by Burt G. Wilder.

  • Burt Green Wilder
Date:
1871
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Licence: Public Domain Mark

Credit: Intermembral homologies : the correspondence of the anterior and posterior limbs of vertebrates / by Burt G. Wilder. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    68/90 (page 66)
    ture and relative position, and I quote a few passages: “ There ex- ists, doubtless, a close general resemblance in the mode of develop- ment of homologous parts; but this is subject to modilication, like the forms, proportions, functions, and very substance of such parts, with- out their essential homological relationships being thereby obliterated. These relationships are mainly, if not wholly, determined by the rel- ative position and connection of the parts, and may exist-independ- ently of form, proportion, substance, function, and similarity of development. But the connections must be sought for at every period of development, and the changes of relative position, if any, during growth, must be compared with the connections which the l)art presents in the classes where vegetative repetition is greatest and adaptive modification least” (20, 174). “ So far is embryology from being a criterion of homology” (63, 1, xxvi). “Embryology afibrds no criterion between ossific centres that have a homological, and those that have a teleological significance” (63, 1, xxv). “No ])art is, however, absolutely autogenous throughout the vertebrate series, and some parts usually exogenous are autogenous in a few in- stances ” (63, 1, 27). “The developmental phenomena of the head neither supersede nor can supply the better evidences of homology afforded by relative position and connections, any more than do those of the foot; ... it is neither here nor elsewhere the cri- terion of homology ” (63, 2, 311). Cleland says, “Morphologically, it is of little importance whether cranial bones are developed in the primordial cartilage, of the skull or around it ” (215, 305). The general importance of embryology in the determination of ho- mologies has been urged by Goodsir and Huxley, ai^d in 251 the lat- ter has well indicated the necessit)' of deciding the general question before attempting to solve minor problems respecting the correspond- ence of the skull and the vertebral column. Agassiz has constantly presented the taxonomic value of embryology not only tlu-oughout his later woi'ks, but in the lectures on Comparative Embryology, Boston, 1849; and upon the ground of a difference of development, he in great measure bases Iris opinion that the Batrachians form a class distinct from the scaly I'eptiles; but in discussing this, Dana asks ^ “ whether, in the determination of classes it is not the more correct method to take note primarily of species in their finished or adult state; and whether adults do not express the true nature and idea of species, or the objects to be classified, rather than the special ' Am. Joiirn. of Sci., Mar. 1864, p. 184