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Natural History: Mollusca. Philip Henry Gosse
Читать онлайн.Название Natural History: Mollusca
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isbn 4064066065522
Автор произведения Philip Henry Gosse
Жанр Документальная литература
Издательство Bookwire
The four Classes of animals which have been considered in the preceding volumes of this series we have seen to have one character in common; viz. the possession of a bony framework within the body, of which a jointed spine is the most essential element. This character, which unites those four Classes into one great group, and gives to that group the name Vertebrata, by which it is distinguished among naturalists, we have seen, however, by slow degrees, deteriorated, if I may use such an expression, from bone to cartilage, and gradually diminished in its development, until, in the lowest of the Fishes, it can scarcely be recognised at all.
I come now to treat of animals in which the bony skeleton no longer exists. The conditions of their existence do not require such a scaffolding on which to build the constituent muscles: many are habitually immersed in water, a fluid the density of which supports their soft bodies; their motions generally lack the precision, energy and variety of those which belong to Vertebrate animals; and where this is not the case, as in the Articulate Classes, the skeleton which affords attachment to the muscles, is not internal, but invests the body, while its substance differs essentially from bone in its chemical composition and its structure.
An immense assemblage of living creatures are included in this category; creatures differing widely from each other in the most important characteristics, so that they cannot be grouped together. The term Invertebrata, by which they are sometimes designated, indicates indeed only a negative character, and we shall be greatly mistaken if we suppose (misled by such a term) that the animals which have a skeleton, and those which are destitute of one, constitute two primary divisions of living beings, of equal or co-ordinate importance.
Several divisions of Invertebrate animals do, in fact, exist, each one of which is equal in rank to the Vertebrata. One of these will form the subject of the present volume, commonly known by the name of Mollusca; a term invented by the illustrious Cuvier, from the word mollis (soft), and evidently suggested by the softness of their boneless bodies. The appellation can scarcely be considered happy, for the character so indicated is very trivial, and is shared by other animals of totally different structure:—objectionable,