A Course Of Elementary Instruction In Practical Biology

Paperback | October 12, 2012

byThomas Henry Huxley

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1889 edition. Excerpt: ...apertures and become lodged in the chambers of the gills, particularly the external ones, which during autumn and winter are completely distended by them and the embryos to which they give rise. Segmentation is holoblastic, and the early developmental phases resemble, in their main features, those already described for the Snail--the original bilateral symmetry is however never disturbed. The embryos when hatched, are so wholly unlike the parent Anodonta, that they were formerly thought to be parasites, and received the name of Glochidium. Each is provided with a bivalve shell, and each valve has the form of an equilateral triangle united by its base with its fellow, by means of an elastic hinge, which tends to keep the two wide open. The apex of the triangle is sharply incurved, and is produced into a strong serrated tooth, so that when the valves approach, these teeth are directed towards one another. The mantle is very thin, and the inner surface of each of its lobes presents three papillae, terminated by fine pencils of hair-like filaments. The oral aperture is wide, and its margins are richly ciliated. There is a single adductor muscle and a rudimentary foot, from which one or two long structureless filaments, representing the byssus of the sea-mussel, proceed. These byssal filaments become entangled with one another and tend to keep the ' Glochi-dia' in their places. The gill-laminae of Anodonta will accommodate some three millions or more of these Glochidia. If the animal is living in company with fish it will eject them, whereupon they attach themselves to floating bodies--very commonly to the tails, fins or gills, of fishes--by digging the incurved points of their valves into the integument in the latter case, and holding on by...

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1889 edition. Excerpt: ...apertures and become lodged in the chambers of the gills, particularly the external ones, which during autumn a...

Format:PaperbackDimensions:154 pages, 9.69 × 7.44 × 0.33 inPublished:October 12, 2012Publisher:General Books LLCLanguage:English

The following ISBNs are associated with this title:

ISBN - 10:0217663192

ISBN - 13:9780217663199

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