On the existence and uses of cilioe in the young of the gasteropodous mollusca, and on the causes of the spiral turn of univalve shells / by R. E. Grant.

Date:
[1826]
Catalogue details

Licence: Public Domain Mark

Credit: On the existence and uses of cilioe in the young of the gasteropodous mollusca, and on the causes of the spiral turn of univalve shells / by R. E. Grant. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    which they adhere to the leaves of fuci till they arrive at ma- tuiity. In such genera as have the ova enveloped only in a soft gelatinous matter, we find a delicate membrane surround- ing each foetus, and inclosing a thin amniotic fluid. In these the cilice are so long, and so rapid in their motions, that the young are seen within the ova revolving continually round their own axis, by striking the cilice against the inside of the containing membrane; and when they escape from the ova, they are carried with great velocity through the water by the vibra- tions of the cilice. I have observed the same appearances in the young of the naked gasteropoda as in the ova of different species of Doris, Eolis, &c. which are inclosed in a soft trans- parent gelatinous matter, and adhere by it to rocks or other solid marine bodies. The young in these genera are likewise surrounded, each by a thin membrane and amniotic fluid. They are seen almost continually revolving round their centre within the ova, and they swim rapidly forward by the action of their cilice when they escape from the ova. In those ge- nera which deposit the young in a general horny cell, as those first described, we find no membrane or amniotic fluid sur- rounding each foetus, but the horny covering is lined with a delicate membrane which incloses the whole of the embryos and the gelatinous fluid in which they are developed. The young of the Buccinum, when mature, escape from the cell, by a part of the horny covering separating on the inner con- cave side of the cell. The young of the Purpura escape by the falling off of a firm gelatinous plug from the free extre- mity of the cell. The portions of the outer covering which fall off are probably loosened by the motions of the young within ; and as the young are still safely lodged in their cells when they first come in contact with the sea water by the for- mation of the aperture, we find the cilice in such genera much less developed than in the other genera without a horny co- vering. Their motions appear destined to bring a constant supply and renewal of pure sea water in contact with the young in the cells, in order to perfect the formation of the shell before their final departure from the now open cavity of the cell. In the ova which are enveloped in a gelatinous connecting matter without any horny covering, we observe