. Evolution and disease . ASCIDIAN NOTOCHORD. Fig, 19.—Ascidian Tadpoles (after Lankester).adult ascidian. A, An many structures and organs are formed and then dis-appear without attaining, as far as our knowledge allowsus to judge, a functional condition. 40 EVOLUTION AND DISEASE. The only interpretation which can be put onthis fact is, that these organs or parts have beenfunctional in the ancestors of such animals, but inconsequence of the increased use of other parts andchange in surrounding conditions, the organs in questionare not so serviceable to the animal and have, inconsequence of di
. Evolution and disease . ASCIDIAN NOTOCHORD. Fig, 19.—Ascidian Tadpoles (after Lankester).adult ascidian. A, An many structures and organs are formed and then dis-appear without attaining, as far as our knowledge allowsus to judge, a functional condition. 40 EVOLUTION AND DISEASE. The only interpretation which can be put onthis fact is, that these organs or parts have beenfunctional in the ancestors of such animals, but inconsequence of the increased use of other parts andchange in surrounding conditions, the organs in questionare not so serviceable to the animal and have, inconsequence of diminished use, slowly but graduallyatrophied. This effect may be conveniently referredto as suppression. It is also a point of some importanceto remember that in consequence of changed con-ditions in the surroundings and habits of an animal,organs originally used for one purpose may becomeso changed that they fulfil quite a different purpose : forexample, the remora, or sucking-fish, is able to attachitself to the shark by means of a sucker
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Keywords: ., bookcentury1800, bookdecade1, booksubjectcongenitalabnormalities
