A few minutes after the crab had been placed in the tumbler, I gave a peep to see how he was getting on. To my intense surprise, I observed that his shell had just opened near the tail! My first feeling was one of sorrow, thinking that in handling the specimen I had been too rough, and had perhaps injured it. This apprehension was soon changed to delight, as I became by degrees aware that exuviation had actually commenced.
The operation did not extend beyond five minutes (although the time appeared much longer to me), and was carried on by gentle, and at first almost imperceptible degrees. The shell, or carapace, was slowly raised over the back, and gave one the idea of the rear view of a lawyer's white wig when tilted over his brow, thus exposing the natural black hair on the occiput below; for, as the body of the animal came forth, it was very dark in colour, while the old case assumed a whitish hue. I need hardly say, the leg sheaths of the crab did not split open, and yet the corresponding limbs were drawn out with the greatest ease. Moreover, they did not appear in view one by one, but in a cluster, as it were, and packed close to the bent body of the crab.
During the entire process the animal appeared to use scarcely any exertion whatever, certainly not half so much as any human being would exhibit in throwing off the most trifling garment. In fact, the crab seemed to swell painlessly, and gently roll or glide out in a kind of ball. Until it had completely escaped from its old shell, I was somewhat puzzled to guess what shape it would eventually assume. The eyes and antennæ, so soon as they left their old sheaths, commenced, together with the flabellæ, to work as usual, although as yet they were still inside the exuvium. This circumstance was distinctly visible by looking through the side of the half-cast shell.
It was a curious and extraordinary sight to see the eyes gradually lose their brilliancy, and exhibit the filmy, lack-lustre-like appearance of death, while the act of exuviation was being accomplished. I may add that the tumbler which held my little captive stood upon a table near a large window, and that the sloughing operation was watched through a powerful hand lens.
On an after and well-remembered occasion, I saw a moderate-sized Partane standing on the top of a bush of Chondrus Crispus that grew in my aquarium. The fronds were attached to a piece of sandstone, placed uppermost upon a cluster of rock-work, situated, as before mentioned, in the centre of the vessel, and rising slightly above the level of the water. Thinking he was planning means of escape, I turned away for a few moments to procure a simple instrument wherewith to carry him to a less elevated position. On my return I saw him in the act of backing out of his shell. It was a singular circumstance that I should have just risen from the perusal of a talented author, who informed me that 'the crab hitches one of its claws into some crack or fissure, and from this point of resistance gives more power in emerging and withdrawing itself from between the carapace and the tail.'
Certainly no statement could more inadequately describe what I had witnessed in both of my crabs. Not only was the whole operation performed with perfect ease, but I am much inclined to believe with a degree of pleasure. For a while one of my crabs stood in juxtaposition to the shadow of its former self, and rubbed his antennæ and wee peeping eyes as if awakening from a sleep. He had been lately, there was no doubt, living in an oppressed state, and might probably have surveyed things around him somewhat darkly, but now all was bright and clear again. On turning, the first object that caught his awakened eye was his cast-off vestment, which he seemed to scan as dubiously as a grown man would an exhumed pair of boyish corduroys, and mutter musingly, while stroking his chin, 'Well, come what will, it can never be my case again.'
On taking it in my hand, the Partane felt quite soft and velvetty to the touch, and exhibited no signs of alarm.
Since then I have repeatedly had shells of crabs cast in smooth glass globes, containing nothing else but clear salt water. This fact, in my opinion, completely subverts the statements of certain writers, who assert that these animals require extraneous assistance when about to exuviate.
Some writers have questioned the truth of the generally-received opinion that the new parts of the crab are derived from the old: that, for instance, a claw is regenerated within a claw, a limb within a limb, eyes within the eyes, and that on exuviation each is withdrawn from the pre-existing organ as from a sheath. But my operations tend fully to confirm the popular and existing belief.
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.