Glimpses of Ocean Life; Or, Rock-Pools and the Lessons they Teach

by John Harper

I will now, however, endeavour as briefly as possible to make the reader acquainted with what has already been written upon exuviation, as far as I have been able to learn, up to the present time, interspersing the narrative with such notes as may seem necessary by way of illustration, and then proceed, in the words of Shakspeare, to lay down my own 'penny of observation.'

The first clear and satisfactory remarks on this subject were made by the celebrated Reaumur, who lived above a century ago: 'The unexampled accuracy and truthfulness of this great naturalist is attested,' says one writer, 'by the fact, that of all the observations made by himself alone, far exceeding those of any other writer of past or present times, and occupying in their published form numerous large quarto volumes, scarcely one has been contravened by subsequent credible observers, whilst they have formed the substance of half the numerous compilations on insect life, acknowledged or otherwise, which have appeared since his time.'

Goldsmith, who derived his knowledge of this subject from Reamur, tells us, in his usual free and easy style, that crustaceous animals (as crabs and lobsters) 'regularly once a year, and about the beginning of May, cast their old shell, and nature supplies them with a new one. Some days before this necessary change takes place, the animal ceases to take its usual food. It then swells itself in an unusual manner, and by this the shell begins to divide at its junctures between the body and the tail. After this, by the same operation, it disengages itself of every part one after the other, each part of the joints bursting longitudinally, till the animal is at perfect liberty. This operation, however, is so violent and painful that many die under it; those which survive are feeble, and their naked muscles soft to the touch, being covered with a thin membrane; but in less than two days this membrane hardens in a surprising manner, and a new shell as impenetrable as the former supplies the place of that laid aside.'

This, then, was and is to a great extent, up to the present time, the universally adopted explanation. Goldie, of course, could not afford time, and it may be doubted if he possessed the requisite amount of patience, to confirm what he wrote by actual observation. Seeing that the statement was graphic in its details, and evidently either wholly or in part the result of personal observation, he very naturally gave it full credence. But what shall we say of a noted writer (Sir C. Bell)[4] who apparently half doubts the truth of exuviation, for although he mentions the particular account which Reamur gives, yet tells his readers that 'naturalists have not found these cast off shells.' After such a remark as this, we need no longer sneer at the compilations of the author of the 'Vicar of Wakefield.'

I need hardly state, that at certain seasons of the year almost every rock-pool at the sea-shore will exhibit to the observant eye scores of 'these cast off shells' in a perfect state. The writer above quoted also remarks, 'We presume the reason that the shells of the crustacea are not found in our museums, is because they are not thrown off at once, but that the portions are detached in succession.' An ill-founded presumption this, the fact being that the inelastic integument is invariably (in all the Decapoda at least) thrown off entire, the eyes and long antennæ sheaths, the claws with the hair attached, even the gastric teeth, all remain with wonderful exactness.

To look at the rejected shell, indeed, any person not previously acquainted with the fact would naturally suppose that he saw before him the living animal, a close inspection being necessary to dispel the illusion. As soon as the crab has emerged from its old covering, it increases with such astounding rapidity, that at the end of one or two days it can grow no larger until the next moulting time.

In referring to my own introduction to the subject of exuviation, I may be allowed to notice the annoyance a young aquarian experiences from the rapidity with which the tank water is apt to become opaque. As such a state involves considerable trouble, especially when the occupants of the tank are the subjects of continued observation, I may mention, in passing, that the means I adopted to correct this state of matters was either to syringe the water frequently, or what seemed to answer still better, to permit it to run off by a syphon into a basin on the floor.

When the opacity of the tank is occasioned by decaying animal matter, the only remedy is to remove the offending 'remains.' But with many of the common inhabitants of the tank—the crustaceans, for example—great difficulty is often experienced in ascertaining their state of health, with a view to sanitary investigation. As these creatures, instead of boldly exhibiting themselves during the day, generally hide under pebbles or pieces of rock, or are buried in the sand, it is sometimes necessary to submit the contents of the mimic rock-pool to a process of 'putting things to rights,' as the ladies say when about doing a kindness,—oh, horror!—to our books and papers.

It happened on a certain occasion that my aquarium was in an unsatisfactory condition. A nasty vapour arose from the base, and diffused itself over nearly the entire vessel. My fishes disliking their usual haunts, were all spread out at full length high and dry upon a ledge of rock-work, projecting above the surface of the water. The little Soldier-Crab had managed to drag his body and heavy tail piece up the brae, hoping to breathe the fresh air in safety. His big brother was not so successful, and despite his efforts speedily came to grief. Finding he could not drag his carriage up the rock, he stepped out of the lumbering vehicle. His appearance soon became woe-begone in the extreme. In a few minutes he expired. The buckies, too, with singular instinct, had collected in a row along the dry ledge of the tank.