File:Evolution and disease (1890) (14577135419).jpg

Identifier: evolutiondisease00blanuoft (find matches)
Title: Evolution and disease
Year: 1890 (1890s)
Authors: Bland-Sutton, John, Sir, 1855-1936
Subjects: Diseases -- Causes and theories of causation Medical genetics Abnormalities, Human Animals -- Abnormalities
Publisher: New York, W. Scott
Contributing Library: Kelly - University of Toronto
Digitizing Sponsor: MSN

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oundas a band of fibrous tissue, and in a few cases absent. In reference to supposed useless parts, Wallace is ofopinion that the assertion of inutility in the case of anyorgan or peculiarity which is not a rudiment or a cor-relation, is not, and never can be, the statement of a factbut merely an expression of our ignorance of its purposeor origin. In the above quotation the term rudimentrefers to such parts as the pineal body, the vermiformappendix, and teeth which are developed but rarely cutthe gum. These are vestiges of organs probably of greatimportance to the ancestors of the forms in which theynow persist as reliqida. It seems highly probable that a VESTIGIAL PARTS. 63 part which has had important functions in an animal,and then has had its function gradually abrogated byanother part, is more prone to be persistent in rudimentthan remnants of organs of less importance. Darwinexpresses this view of the matter thus : Organs nowof trifling importance have probably been of high im-
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FiG. 31.—A Homed Sheep with cervical auricles. portance to an early progenitor, and, after being slowlyperfected at a former period, have been transmitted toexisting species in nearly the same state, although nowof slight use. That mere disuse is insufficient to pro-duce abolition of a part is illustrated in a strikingmanner by the cervical auricles in goats, pig, and man.These ears or auricles, in so far as we know, subserve no 64 EVOLUTION AND DISEASE. useful purpose, are extremely variable, occur in bothsexes, and often are of large size (fig. 30- Theseauricles, as will be shown in detail subsequently, areenlarged opercula, )et an enormous space of time haselapsed since the gill-slit they guarded were functional.Nevertheless they illustrate the view I am advoca-ting, for gill-slits and opercula were of high functionalimportance in the ancestors of mammalia, and are stillconspicuous in the early embryo. As cervical ears orauricles will occupy our attention at some length presently

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