Crab has another method of getting at the cocoa-nut, and displays an instinctive knowledge of political economy which is very remarkable.

"These animals live under the cocoa-nut-trees, and subsist upon the fruit which they find upon the ground. With their powerful front claws they tear off the fibrous husk; afterward, inserting one of the sharp points of the same into a hole at the end of the nut, they beat it with violence against a stone until it cracks; the shell is then easily pulled to pieces, and the precious fruit within devoured at leisure. Sometimes, by widening the hole with one of their round, gimlet claws, or enlarging the breach with their forceps, they effect sufficient entrance to enable them to scoop out the kernel, without the trouble of breaking the unwieldy nut.

"These crabs burrow in the earth, under the roots of the trees that furnish them with provisions-prudently storing up in their hóles large quantities of cocoa-nuts, stripped of their husk, at those times when the fruits are most abundant, against the recurring intervals when they are scarce. We are informed that if the long and delicate antennæ of these robust creatures be touched with oil, they instantly die. They are not found on any of these isl ands except the small coral ones, of which they are the principal occupants. The people here account them delicious food."

The palm-climbing habits of the Robber Crab are mentioned by Mr. T. H. Hood, in his "Notes of a Cruise in H. M. S. Fawn, in the Western Pacific." In the Samoan group of islands, the crab is called "Ou-ou," and is a favorite article of food. While the vessel remained off Samoa, Mr. Hood asked about these crabs; and though he did not see any of them performing so strange a feat, he shows that there are very good grounds for believing the possibility of such an action.

"I inquired of them about the habits of the Ou-ou, or great cocoa-nut-eating crab, common here, and found the reports previously received from the natives corroborated. Mr. Darwin mentions that, in the Seychelles and elsewhere, there is a species which is in the habit of husking the nuts on the ground, and then tapping one of the eyes with its great claw, in order to reach the kernel. Its congener here ascends the cocoa-trees, and having thrown the nuts down, husks them on the ground; this operation performed, again ascends with the nuts, which he throws down, generally breaking them at the first attempt, but, if not successful, repeating it till the object is attained.

"Before leaving, an old Savage Island man at the mission brought in three or four immense Ou-ous, which evinced in their efforts to escape, bursting coils of cocoa-nut sinnet, a strength quite sufficient to husk the toughest cocoa-nut. As to the method of obtaining the contents afterward, every native (both Samoans and Niuans) confirms the account mentioned before. The Niuans understand their habits best. The old man who brought them to-day dug them out of the holes in which they remain many weeks torpid. The female differs from the male in having three flippers, well furnished with strong borers, on the right side of the sac.'

When full grown, this crab is more than two feet in length, and, as may be seen by the illustration, is stoutly made in proportion to its length. The color of the creature is very pale brown, with a decided tinge of yellow.

PASSING by many other species of crustacea which burrow in the earth, or mud, or sand, we come to a very remarkable being, which makes its habitation in solid wood. This is the WOODBORING SHRIMP (Chelura terebrans), one of the sessile-eyed crustacea, nearly related to the well-known sand-hopper, which is so plentiful on our coasts.

Although very small, it is terribly destructive, and does no small damage to wooden piles driven into the bed of the sea. It is furnished with a peculiar rasping instrument, by means of which it is enabled to scrape away the wood and form a little burrow, in which it resides, and which supplies it with nourishment as well as with a residence. The tunnels which it makes are mostly driven in an oblique direction; so that when a large number of these creatures have been at work upon a piece of timber, the effect of their united labors is to loosen a flake of variable dimensions. As long as the weather is calm, the loosened flake keeps its position; but no sooner does a tempest arise, than the flake is washed away, and a new surface is exposed to the action of the Chelura.

When the Chelura is placed on dry land, it is able to leap nearly as well as the sand-hopper, and performs the feat in a similar manner.

THIS is not the only wood-boring crustacean with which our coasts are pestered; for the GRIBBLE (Limnoria tenebrans) makes

deeper tunnels than the preceding creature, though it is not so rapidly destructive, owing to the direction of its burrows, which are driven straight into the wood, and do not cause it to flake off so quickly as is the case when the Chelura excavates it. Still, it works very great harm to the submerged timber, boring to a depth of two inches, and nearly always tunneling in a straight line, unless forced to deviate by a nail, a knot, or similar obstacle. The Gribble is a very tiny creature, hardly larger than a grain of rice, and yet, by dint of swarming numbers, it is able to consume the wooden piles on which certain piers and jetties are supported; and in the short space of three years these destructive crustacea have been known to eat away a thick fir plank, and to reduce it to a mere honey-comb. Sometimes these two wood-boring shrimps attack the same piece of wood, and, in such cases, the mischief which they perpetrate is almost incredible, considering their small dimensions and the nature of the substance into which they bore. The common fresh-water shrimp, so plentiful in our brooks and rivulets, is closely allied to the Gribble, and will convey a very good idea of its appearance. In some parts of our coasts the ravages of these animals are so destructive, that the substitution of iron or stone for wood has become a necessity.

H

CHAPTER V.

BURROWING MOLLUSKS.

The BORING SNAIL of the Bois des Roches.-Opinions as to its Method of Burrowing.-Shape of the Tunnels.-Solitary Habits of the Snail.-The PIDDOCK, its Habits and Appearance.-Structure of the Shell, and its probable Use.-Method of Burrowing.-Use of the Piddock and other marine Burrowers.-The Balance of Nature preserved.-The WOOD-BORER and its Habits.-The DATE SHELL.-Its extraordinary Powers of Tunneling. The RAZOR SHELL.-Its Localities and Mode of Life.-The FLASK SHELL and the WATERING-POT SHELL.-The SHIPWORM.-Its Appearance when Young and Adult.—Its curious Development.— Its Ravages, and the best Method of checking them.-Its Value to Engineers. -The GIANT TEREDO.-Form, Dimensions, and Structure of the Shell.-How and where discovered.

ILL fitted as the Mollusks seem to be for the task of burrowing, there are several species which are able not only to make their way through soft mud, or into the sandy bed of the sea, but to bore deep permanent tunnels into stone and wood. Even the hard limestone and sound heart-of-oak timber can not defy these indefatigable laborers, and, as the sailor or the dweller on the coast knows full well, the rocks and the timber are often found reduced to a mere honey-combed or spongy texture by the innumerable burrows of these mollusks.

THERE is now before me a piece of very hard calcareous rock, in which are bored several deep holes, large enough to admit a man's thumb, and remarkably smooth in the interior, the extremity being always rounded. Indeed, if a hole were made in a large lump of putty by putting the thumb into it and turning it until the sides of the hole became smooth, a very good imitation of these miniature tunnels would be produced. This fragment of stone was taken from a little wood in Picardy, called Le Bois des Roches, on account of the rocky masses that protrude through its soil, and was brought to England by Mr. H. J. B. Hancock, who kindly presented it to me.

In the winter time, each of these holes is occupied by a specimen of the Helix saxicava, a small snail, closely resembling the common banded snail of our hedges (Helix nemoralis), and it is thought that the holes are excavated by the snail which inhabits

them. Mr. Hancock, who has lately reopened in the columns of the Field newspaper a controversy respecting these snails, which was initiated in 1839, is of opinion that the snails really form the hole, and that they burrow at the average rate of half an inch per annum. The late Dean Buckland was of the same opinion. Other naturalists, however, think that the holes were originally excavated by pholades and other marine mollusks when the rocks in question formed part of the ocean bed, and that the snails merely inhabit the ready-formed holes. Mr. Pinkerton upholds this opinion, and states that at least three other species of helix possess similar habits, the garden and the banded snail being among the number.

I have compared the burrows of the mollusk, which we will call the Boring Snail, with those of the pholas and lithodomus, both of which will be presently described, and find that there is no resemblance in their forms, the shape and direction of the holes being evidently caused by an animal of no great length in proportion to its width. In my own specimen, every hole is contracted at irregular intervals, forming a succession of rounded hollows. If we return to our lump of putty, we may form the holes made by the thumb into a very good imitation of those in which the Boring Snail lives. After the thumb has been pushed into the putty and well twisted round, put in the forefinger as far as the first joint and turn it round so as to make a rounded hollow. Push the finger into the hole as far as the second joint, and repeat the process. Now introduce the whole of the finger, enlarge the extremity of the hole and round it carefully, when there will be a very correct representation of the tunnel formed in the rock.

Granting that the snail really does form the burrow, we have still to discover the mode of working. Mr. Hancock says that it must do so by means of an acid secretion proceeding from the foot, which corrodes the rock and renders it easy to be washed away. If the snail be removed and placed on litmus paper, the ruddy violet color which at once tinges the paper shows that there is acid of some kind, and if the paper be applied to the spot whence the snail has been taken, the same results follow. It is a remarkable fact that although the snail ⚫ leaves the usual slimy marks of its progress when crawling in the summer time, no mucus is perceptible on the approach of winter. When the cold months come round, the Boring Snail