On Whales, Past and Present, and Their Probable Origin: A Discourse (Classic Reprint) - Softcover

Flower, W. H.

Softcover

ISBN 10: 0282908315 ISBN 13: 9780282908317

Verlag: Forgotten Books, 2017

Inhaltsangabe

Excerpt from On Whales, Past and Present, and Their Probable Origin: A Discourse

In the organs of the senses the Cetacea exhibit some remarkable adaptive modifications of structures essentially formed on the Mam malian type, and not on that characteristic of the truly aquatic Vertebrates, the fishes, which, if function were the only factor in the production of structure, they might be supposed to resemble.

The modifications of the organs of sight do not so much affect the eyeball as the accessory apparatus. To an animal whose surface is always bathed with fluid, the complex arrangement which mammals generally possess for keeping the surface of the transparent cornea moist and protected, the movable lids, the nictitating membrane, the lachrymal gland, and the arrangements for collecting and removing the superfluous tears when they have served their function cannot be needed, and hence we find these parts in a most rudimentary condition or altogether absent. In the same way the organ of hearing in its essential structure is entirely mammalian, having not only the sacculi and semicircular canals common to all but the lowest vertebrates, but the cochlea, and tympanic cavity with its ossicles and membrane, all, however, buried deep in the solid substance of the head; while the parts specially belonging to terrestrial mammals, those which collect the vibrations of the sound travelling through air, the pinna and the tube which conveys it to the sentient structures within are entirely or practically wanting. Of the pinna or external ear there is no trace. The meatus auditorius is certainly there, reduced to a minute aperture in the Skin like a hole made by the prick of a pin, and leading to a tube so fine and long that it cannot be a passage for either air or water, and therefore can have no appreciable function in connection with the organ of hearing, and must be classed with the other numerous rudimentary structures that whales exhibit.

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Details zur Ausgabe

• Verlag: Forgotten Books
• Erscheinungsdatum: 2017
• Sprache: Englisch
• ISBN 10: 0282908315
• ISBN 13: 9780282908317
• Einband: Taschenbuch
• Anzahl der Seiten: 26
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