added to (in certain definite directions) slowly yet not continuously, instead of the whole being formed at a single period. [24] In the genus Alcippe, and in Cryptophialus, the whole of the external membranes are moulted, excepting the surface of attachment; but then these Cirripedes live in cavities which they form for themselves, and are thus protected. In Lithotrya the membrane of the peduncle, with its little valves or scales, is moulted, but here, again, this very part is protected by the tubular cavity, which the animal forms and inhabits. Neither of these three genera belong to the Balanidæ, or sessile Cirripedes, which we are now more especially describing. If, now, a section of one of the shelly zones of growth be carefully examined, it can in some cases be distinctly seen to be formed of successive, excessively fine laminæ; but the animalised tissue (which differs much in amount in different Cirripedes) left after the shell has been dissolved in acid, exhibits, in most cases, neither laminæ nor any other structure whatever. The shell seems to be the actual pulpy corium, or true skin, in a calcified condition, but generally with its cellular structure modified and much reduced: I have taken a bit of recently-formed shell of Tetraclita and of Coronula, with the corium still adherent to its under surface, and after dissolution in acid, I could not distinguish the part, which had just before existed as shell, from the corium itself. In the case of Coronula, immediately prior to the period of moulting and growth, I found the unaltered corium so charged, as to effervesce, with carbonate of lime, either in a state of dissolution, or in granules too minute to be visible under the highest powers.