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of development is that there are many vacant places in the polity of nature, and that development takes place in that direction which fits the creature to occupy a vacant place, and is, therefore, diverse. It seems to me that this--the only answer that can he given--is necessarily a modified form or mode _of creation._ How can _natural causes_ know anything about a polity of nature and a vacant place, here and there, so that the creature must develop in one way or another to fill it? Another set of cases is the production of similar functional results by most diverse means, as in the case of flying animals, birds, pterodactyles, and bats; here there is a widely different modification of the fore-arm and other bones, all for the same purpose. The reader will do well to refer to Mr. Mivart's book on this subject. Again, the question of types seems to be pointed to in the curious fact of what I may call the double development of birds from reptiles. Mr. Mivart says, "If one set of birds sprang from one set of reptiles and another set from another set of reptiles, the two sets could never by 'natural selection' only have grown into such perfect similarity." Yet we can trace the _Struthious_ birds (those that, like ostriches, do not fly) through the Dinosaurs and _Dinornis_, and the flying Carinate birds though pterodactyles, _Archaeopteryx_, and _Icthyornis_, &c. It might well be added to this part of the subject, that granted that developmental changes were often small, that progress was attained little by little, this does not appear to have been always the case. The discoveries of the fossil species of horse,[1] _Eohippus, Hipparion_, and so forth, clearly establish a developmental series, and the ancient forms are claimed as the ancestor of the modern horse; but these (Professor Owen tells us) differed more from one another than the ass and the zebra (for instance) differ from the horse. Still, of course it may be that there are still undiscovered intermediate forms; and in any case there need be no desire to detract from the value of the series, as really pointing towards a gradual perfection of the horse from a ruder ancestor up to the latest type. But having reached the type, and though that type exhibits such (considerable) variations as occur between the Shetland pony, the Arab, and the dray-horse, we have still no difficulty in recognizing the essential identity; nor is there any evidence or any probabil
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