The Doctrine of Evolution - Its Basis and Its Scope by Henry Edward Crampton
page 50 of 313 (15%)
page 50 of 313 (15%)
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having constant vibratile processes, or shells of some kind, while in
still other cases like individuals combine to make colonies which are more or less definite and permanent. Here at the very foot of the organic scale are found animals which seem to be entirely different from those above. Upon examination they, like _Hydra_, prove to be the same as regards the number and kind of functions they perform, but in structural regards their evolutionary relation to all higher animals is indicated solely by the fact that they are cells composed of protoplasm. Nevertheless the principle which states that resemblance means consanguinity still holds true, for cellular constitution is a unique possession of things of the living world,--something which demonstrates the common origin of all living things just as truly as the "cat-_ness_" of our first series of examples reveals for a smaller group the significance of likeness and the nature of the basic law of comparative anatomy. * * * * * Employing a figure of speech, we have climbed down the animal tree from the higher regions where the mammals belong. Having reached the very foot of the trunk we are in a position to review and summarize the evidences which we have discovered all about us as we have descended. The various examples we have mentioned and the groups to which they belong clearly occupy different places in the scale which begins with the protozoa and extends upward to the most complicated and differentiated animals. _Hydra_ takes its place above the protozoa for obvious structural reasons; worms belong to a still higher zone, surpassed by the more complex jointed animals like crustacea and insects. Far above these are the vertebrates, among which we have already demonstrated the occurrence of different grades of organization, from the fish up to the higher amphibia and reptiles, and beyond in two directions to the diverging birds and mammals. |
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