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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    body, and consequently the shell, to assume a curved form, with the heart always on the convex side of the curve. The heart pulsates about twenty times in a minute, and the dias- tole of its cavities is much more sudden and remarkable than the systole. If the motions of the heart were the only powers which turned the body from a straight line, the spire of the Buccinum would revolve on the same plane round its shut ex- tremity, like that of a Spirorhis ; but as the animal’s foot re- quires continually to descend over the columella of the shell, before it can reach a solid surface to creep upon, the body and the shell are thus incessantly deflected from the original plane, and forced to assume the spiral form which we observe in the adult Buccinum, and in most univalve shells. In the reverse shells, where the cone lies on the left side of the ani- mal, we likewise find the heart in a reverse situation, being then on the right side. The two wide projecting circles of. cilice at the sides of the mouth continue visible for some time after the escape of the young Buccinum from the general cell, and they are of such length and size that their motions can be easily followed by the eye aided by the microscope. The young of the Purpura lapillus are also inclosed in a horny general capsule, like those of the Buccinum. The ovum of the Purpura is shaped like a grain of corn, while that of the Buc- cinum is flat like a split pea. When first deposited, the horny covering in both is white and soft, but soon becomes yellow and firm, and the transparent gelatinous matter enveloping the young becomes gradually thinner as the young advance to maturity. There are about fifty-five young in each cell of the Purpura, and they exhibit the same mode of develope- mentas those of the Buccinum; the same revolution of particles within the transparent part of the embryo give the first indi- cation of life, and the same wide ciliated opening is seen on each side of the head, the cilice continuing to vibrate for some time after the escape of the young from the cell or ovum, as in the Buccinum. These circles of long vibrating cilice I have also met with in the young of other genera of testaceous mollusca, as the Trochus, Nerita, &c. which are not inclosed in a general horny cell, but are merely enveloped in a soft gelatinous matter, by