Structure and Classification of Zoophytes (Classic Reprint) - Hardcover

James D. Dana

9780364949481: Structure and Classification of Zoophytes (Classic Reprint)

Hardcover

ISBN 10: 0364949481 ISBN 13: 9780364949481

Publisher: Forgotten Books, 2018

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Excerpt from Structure and Classification of Zoophytes

The mind should be disabused of the idea that all polyps form coral. There are many species identical in general structure with coral animals by which no coral is secreted. Among these, are the Actinia - common on some parts of our own coasts, - many of which are richly coloured and occasionally measure several inches in diame ter, as is well shown by the drawings of Mr. Drayton on the first five plates of the Atlas. Other species contain scattered granules of lime. Thus there is a gradual passage up to the coral-making species, whose secretions form a solid framework to the animal.

Another simple fact should be here understood. On examining any piece of coral, the surface is found to be covered either with pro minent cells, or concave depressions; hundreds, perhaps, to a single branch. Each of these cells marks the position of a polyp, and counting them we may ascertain the number of ﬂower-animals that together constructed the branch. But this compound structure is not universal. Some coral-polyps are single animals, each a separate individual like the soft Actinia; and this is apparent in the coral, for it presents but a single cell or depression. From the solitary polyp, there are all possible varieties among zoophytes, up to living masses, in which hundreds of thousands are congregated, all the progeny of a single germ.

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