The Doctrine of Evolution - Its Basis and Its Scope by Henry Edward Crampton
page 43 of 313 (13%)
page 43 of 313 (13%)
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Even more obvious is the change of structure in the case of masts of
vessels, which originally bore the sails for propelling the ship. When steam engines were employed to give motive power, masts did not disappear. They now provide the derrick supports of trading steamers; in battleships their function is changed to that of fighting tops and signal yards. Even the poles carried by canal boats to bear windmills must be regarded as the reduced vestiges of masts originally constructed to carry sails; and their adaptive evolution, like that of countless structures in animals, has been accomplished by degeneration. * * * * * The birds are another class of backboned animals which exhibit identical principles of relationship. A heron has long legs and wide-spreading toes, which keep its body out of the water as it stalks about the marshes where it seeks its food; its bill is a long slender pincers. Compare it with an eagle; the latter has a short and heavily hooked beak to tear flesh, while its stout legs bear strongly curved talons to hold its struggling prey. Swimming birds like the swan and duck and loon possess feet which are constructed in general like those of the former examples, but they are webbed and shortened to serve as paddles. In the penguin we find a counterpart of the seal among mammals; its feathers are much reduced and its fore limbs are no longer wings enabling the animal to fly, but they are paddles which it uses when it swims in pursuit of fish. Finally the ostrich and wingless bird of New Zealand--the _Apteryx_--have wings that are useless vestiges, which, in the latter case, are hidden under the brushlike feathers covering the body. It is unnecessary to add more examples, for even these few illustrations establish exactly the same principles of relationship and evidences of evolution that are to be found in the series of mammalia. |
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