. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 626 CILIA. Such is an outline of the observations hitherto made relative to the ciliary motion in the bivalve Mollusca. We may now shortly con- sider those which refer to the other classes of these animals. Dr. Fleming,* in describing the cilia in some species of Polypi, states that " analo- gous hairs" exist on the branchiae of the Tri- tonia, which may probably be considered as forming part of the aerating organs. He also mentions, in another place,f that these branchiae " readily fall off, and, as if in
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 626 CILIA. Such is an outline of the observations hitherto made relative to the ciliary motion in the bivalve Mollusca. We may now shortly con- sider those which refer to the other classes of these animals. Dr. Fleming,* in describing the cilia in some species of Polypi, states that " analo- gous hairs" exist on the branchiae of the Tri- tonia, which may probably be considered as forming part of the aerating organs. He also mentions, in another place,f that these branchiae " readily fall off, and, as if indepen- dent, are capable of swimming about for a short time in the water, by means of minute hairs with which their surface is covered, and which move rapidly, pushing forwards the distal ; Gruithuisen, as formerly mentioned, observed the ciliary motion, and recognised its true nature in the Valvata bran- chiata, a species of fresh-water snail. Also Itaspail,} having seen the phenomena pro- duced by the gills of the Fresh-water Mussel, was led by analogy to discover the same in the Lymnaea and Paludina. Without being aware of these previous researches, I observed the ciliary motion in several different tribes of marine Mollusca, and shewed that it prevailed extensively among Mollusca generally. Mr. Lister, as has been already stated, has subse- quently discovered that it exists in the Ascidia; and since then I have also found it in that animal, though in a different species. 9. Of the, ciliary motion of the embryo of Mollusca.—The embryo of Mollusca exhibits, while within the egg, a peculiar rotatory mo- tion which belongs to the class of phenomena we are here considering, and is referable to the same cause. This motion has been observed in the Gasteropodous and Bivalve Mollusca, and may perhaps be found in others. Gasteropoda.—Swammerdam§ states that in examining the young of the viviparous water- snail, while they were yet inclosed in the mem- branes of t
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