File:Image from page 54 of "Evolution and disease" (1890) (14577141068).jpg

Identifier: evolutiondisease00blanuoft 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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Text Appearing Before Image: nuous pressure. It will there-fore be instructive as well as conducive to clearness todescribe some typical cases of the various forms ofatrophy. Atrophy from changed habits.—Among the manyanomalies of animal life in New Zealand must be in-cluded the remarkable owl-parrot or kakapoe {StringopsJiabroptilus). This bird is nocturnal in its habits, feedson fern-shoot, roots, berries, and, it is said, occasionallylizards. It climbs but does not fly, though possessing 36 EVOLUTION AND DISEASE. what looks like, in so far as shape and size are con-cerned, an admirable pair of wings. A dissection ofthe pectoral muscles is suggestive, for they are thin,flat, and contain but little contractile tissue. Theprominent keel so conspicuous on the sternum of fly-ing birds is, in Stringops, a mere ridge. The intrinsicmuscles of the wings are pale, thin, and composedlargely of fibrous tissue (fig. 17). It has been inferred that these birds have not longbeen inhabitants of New Zealand only, but were de-

Text Appearing After Image: FiG. 17.—The Owl-parrot, or Kakapoe [Stringops habroptihcs). veloped in other countries where their wings were ofuse to them. The disuse of the wings is due to altera-tion in environment. The atrophied wing muscles in the owl-parrot recallthe observations of Rengger who attributes the thin legsand thick arms of the Payaguas Indians to successivegenerations having passed nearly the whole of their livesin canoes with their lower extremities motionless. Atrophy of parts useful for a brief period.—Verymany organs are useful for a brief period, and later VISUSE AND ITS EFFECTS. 37 atrophy or even disappear. The curious suctorial discof the recently hatched embryo of the fish, lepidosteus,is a case in point. In the adult fish the upper jaw endsin a fleshy globular projection ; this, in the embryo, isa large disc, as in fig. i8. Agassiz, to whom we areindebted for much of our knowledge of this structure, hasascertained that the disc is formed two or three daysbefore hatching, and the you

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