Ihey are long, slender, and terminate at each end in a sharpened point, at the base of which is a prominent rim; the terminations thus resemble the pointed stopper and neck of a decanter. Between the extremities the body is straight; but there are on different parts minute cells, sometimes arranged in pairs, sometimes in circles, and occasionally in a spiral manner. If still further decomposed, these bodies become reduced in size, and altered in shape, so as to resemble minute Florence flasks, and finally become resolved into minute globular cells, which constitute the ultimate structure of the membrane. The union of these cells is of the most intimate kind, for with the most powerful and varied lights their points of union could not be detected, till they had become partially decomposed. The dark and light lines with which the membrane is striated, are formed by the more close or loose aggregation of these bodies, as was proved in their decomposition.
The membrane of the axis it is not always easy to demonstrate; sometimes it is very clearly to be seen, and so loosely attached that it may be torn off, either with a knife or by the fingers; at others, so firmly attached and obscure, that its existence would be denied but for its occasional well-marked presence. When the rugae are well marked the membrane is easily observed; when the axis is polished it is very obscure, and is more or less marked, as one or the other preponderates. When the rugae are well marked, they appear to be formed of hollow tubes, which communicate with the tubes of the fleshy bark. These tubes can never be seen to advantage, and frequently cannot be seen at all, unless the specimen be examined in a living state. This membrane is also fibrous, and rends freely in a longitudinal direction. It is longitudinally striated with light and dark lines, as is also observed in the membrane of the bark. The resemblance between these membranes is very great; both are longitudinally striped, both have oval openings, and both have the same ultimate structure. The structure, however, of the membrane of the axis, from its being so firm and horny, is not so clearly to be noticed as of the membrane of the crust. When it is but loosely attached it is observable under the microscope, but it becomes more obscure as its attachment becomes firmer, and when the axis is polished it is not observable at all.
At certain periods, which seem favourable to the growth of this species, when it rapidly increases in size and height, the branches, especially the youngest, are very frequently disfigured with large globular protuberances. These excrescences are to be found at all sea-
