There is yet one curious point connected with this subject which requires explanation, as it is not generally understood. I allude to the apparent disproportionate smallness of the 'glassy bag,' situated at the stump, as compared with the size of the regenerated limb, which is supposed to be folded up within the bag previous to exuviation. On looking at the newly-formed member, we can scarcely believe it possible that the transparent case could by any possibility have held it. The mystery vanishes if the new limb or claw be examined; for, although in shape it is perfect, even to the most minute particular, it remains for a certain period comparatively useless to the animal, from the fact of its being utterly devoid of flesh. The new limb, therefore, can be considered merely as an expanded case, which, by a wonderful law of nature, becomes slowly filled up and completed. Immediately after exuviation has taken place, and a claw is introduced in the place of some mutilated stump, if any one will pull off the new member, he can readily confirm the truth of what I have stated, and, moreover, be able to test into how very small bulk the new limb may be rolled. As the reader may remember, Goldsmith states that the crab casts its shell 'regularly once a-year, at the beginning of May.' Professor Owen fixes the date in the month of August. Professor Bell states, that 'there is no doubt exuviation takes place _annually_ with great regularity, until the growth is completed, which, in many species, is not before the animal is many years old.' Another professor, treating on the same subject, thus writes, 'We are told that all this coat of mail is _annually_ thrown off in a single piece by the contained animal,--the great proficient in Chinese puzzles may well be posed at this greater puzzle.' In fact, all writers whose works I have had opportunity of examining repeat the statement. Mr. Ball, who writes from personal observation, apparently confirms beyond a doubt, the annual moult of Crustacea. This gentleman, we learn, kept a Cray-fish alive for two years in a vase, and found that _during each year its exuvium was shed but once_. It may readily be believed, with such a formidable array of contrary evidence, that I offer my own observations with modesty. But at the same time, I feel justified in confidently stating that the moult of the crab, (in its comparatively youthful state, at all events), takes place not only once, but many times during each year of its existence. My specimens may, perhaps, be considered exceptions to the general rule, but the facts I relate cannot by any possibility admit of doubt. The cast-off shells lie before me as I write.