from any loose materials that are within reach, and has by this means earned its specific name of modiolina.

In two remarkable genera the shell is very small and is cemented to the base of a long shelly tube, through which the siphon runs. The Clavagella is remarkable for the successive. frills that decorate the tube; from three to six of these curious appendages being seen in various specimens. These frills are formed by the orifice of the siphon when the tube is elongated. It is a remarkable fact, that the left valve of the shell is always cemented to the side of the burrow, so that the animal possesses no locomotive power, and in all cases the shell is very small, and sometimes scarcely visible.

The WATERING-POT SHELL (Aspergillum), is well known to conchologists. In this creature the shell is exceedingly small, and so deeply sunk into the tube that only the umbo of each valve is visible. The base of the tube is expanded into a rounded and perforated disc, which bears a remarkable resemblance to the "rose" of a watering-pot, and its opposite extremity is mostly decorated with frills, from one to eight in number.

THE reader will remember that the wood-boring pholas always makes its burrow across the grain of the timber which it is commissioned to destroy. The SHIPWORM (Teredo navalis), on the contrary, always burrows with the grain, and never makes a transverse tunnel, unless turned from its course by some obstacle, such as a nail, or the burrow of another Teredo.

At first sight, few would perceive that the Shipworm belongs to the same class as the oyster and the snail, for it is long, slender, and worm-like in shape, from six to eight lines in diameter, and nearly a foot in length. One end is rather larger than the shaft, if we may use the term, and is furnished with a pair of curved and very narrow shell-valves, while the other is divided into a forked apparatus containing the siphon. The colour is greyish-white.

Such is the aspect of the Shipworm when adult, but in its early stages of existence it possesses a totally different form. When it first issues from the sheltering mantle of its parent, it is a little, round, lively object, covered with cilia, like a very minute hedgehog, and, by the continual movement of these

It does not,

appendages, passing rapidly through the water. however, retain this form for more than six and thirty hours, but undergoes a further process of development, and is then furnished with a distinct apparatus for swimming and crawling. It also possesses rudimentary eyes, and in that portion of the body which may be considered the head, there are organs of hearing resembling those of certain molluscs. When it has passed its full time in this stage of development, it fixes upon some favourable locality, and then undergoes its last change, which transforms it into the worm-like mollusc with which naturalists are so familiar.

The ravages committed by this creature are almost incredible Wood of every description is devoured by the Shipworm, whose tunnels are frequently placed so closely together that the partition between them is not thicker than the paper on which this account is printed. As the Teredo bores, it lines the tunnel with a thin shell of calcareous matter, thus presenting a remarkable resemblance to the habits of the white ant. When the Teredos

have taken entire possession of a piece of timber, they destroy it so completely, that if the shelly lining were removed from the wood, and each weighed separately, the mineral substance would equal the vegetable in weight.

The Shipworm has been the cause of numerous wrecks, for it

silently and unsuspectedly reduces the plankings and timbers to such a state of fragility, that when struck by the side of a vessel, or even by an ordinary boat, large fragments will be broken off. I have now before me two specimens of "wormcaten" timber, one of which is so honeycombed by this destructive mollusc, that a rough grasp of the hand would easily crush it. Yet this fragment formed part of a pier on which might have depended a hundred lives, and which was so stealthily sapped by the submarine miners, that its unsound state was only discovered by an accident.

The copper sheathing, with which the bottoms of ships are covered, is placed upon them for the express purpose of baffling the Shipworm, and though so expensive a process, is cheaper than permitting the destructive creature to work its own will on the vessel. It is possible, however, that an equally effectual, and very much cheaper method of protecting ships and submerged timber may soon be brought into active operation. M. de Quatrefages has discovered that mercurial salts of any kind are instantaneously fatal to the Shipworm, and that, by their use, not only the existing animals may be killed, but their eggs destroyed also. A vessel that has been attacked by these pests may be rid of them by throwing a few pounds of corrosive sublimate into the dock where she lies, and it would not be very difficult to keep a special dock for the purpose.

The most effectual method, however, of checking the ravages of the Shipworm is, by saturating the timber with corrosive sublimate; a process which is effected by exposing the timber for a long period of time, so as to allow the sap to escape, and then by forcing a solution of the metallic poison into the minute interstices of the wood. This is done in a curiously simple manner, namely, by laying the logs of timber on the ground, introducing a tube into one end, carrying the tube to a height of forty or fifty feet, and then connecting it with a tank filled with the solution. It is, of course, necessary that the timber should be thoroughly seasoned before it is thus treated. M. de Quatrefages suggests that the prepared wood might be sawn into thin planks, which could then be used in the same manner as the copper sheathing now in use.

Another species of the same genus, Teredo corniformis, is remarkable for the locality in which it is found. This curious

mollusc burrows into the husks of cocoa-nuts, and other thick woody fruits which may be found floating in the tropical seas. In consequence of the locality which it selects for its habitation, it cannot proceed in one direction for any great distance, and is obliged to make its burrows in a crooked form, which has earned for the creature the specific title of corniformis, or horn-shaped. Fossil woods are often found perforated with these burrows.

Destructive as it may be, the Shipworm will ever be an object of interest to Englishmen, inasmuch as its shell-lined burrow gave to Sir I. Brunel the idea which was afterwards so efficiently carried out in the Thames Tunnel. And, though from the alteration of surrounding circumstances, that wonderful monument of engineering skill has not been so practically useful as was anticipated, it has proved of incalculable value as pioneer to the numerous railway tunnels of this and other countries.

The largest species of this curious genus is the GIANT TEREDO (Teredo gigantea), which produces a shell more than five feet in length, and three inches in diameter. The substance of the shell is of very great strength, being about half an inch in thickness, radiated in structure, and so hard that when the first specimen was brought to England many naturalists took it for a hollow stalactite.

ease.

This creature is a burrower into mud, and was discovered in a very curious manner. In the year 1797, a violent shock of earthquake took place in Sumatra, and caused great upheavals of earth and corresponding floods of water. When the sea receded from one of the bays, certain unknown objects were seen protruding from its muddy bed, and were pulled out with tolerable They projected about eight or ten inches from the mud, and as the projecting portions were beset by serpulæ, bivalves, and other marine parasites, it was evident that they were not forced out of the mud by the shock, but had been in that position for a considerable time. All, however, were damaged, one or both ends being broken off. Their colour was pure white on the exterior, and yellowish within. None of them were perfectly straight, and the greater number more or less contorted.

CHAPTER VI.

BURROWING SPIDERS.

The SCORPION and its habits-The burrow of the Scorpion-How detectedSuicide among the Scorpions-Spiders and their burrows-The Atypus Madame Merian and her book of the BIRD SPIDER-Mr. Bates' Discoveries -Hair of the Bird Spider-The TARANTULA-Its ferocity and courage--The TRAP-DOOR SPIDER-Its tunnel and the lining thereof-Its appearance under the microscope-The "Trap-door" itself, and its structure-Curious example of instinct — Activity of the Spider-Specimen in the British Museum-Strength and obstinacy of the Trap-door Spider-An Australian Trap-door Spider.

AMONG the burrowers belonging to this order may be reckoned the well-known SCORPION, of which there are several species, resembling each other in their general appearance, their structure and their habits.

Scorpions are found in all the warmer portions of the globe, and under the tropics they may be said to swarm. They are, as a general rule, intolerant of light, creeping by day into every cranny that can shelter them from the unwelcome sunbeams, and often causing very great annoyance by this custom. Old travellers, who have learned by experience the habits of these creatures, do not retire to rest before they have carefully examined the bed and surrounding furniture, especially taking up the pillow, and seeing that no enemy has lodged within the folds of the bedding. The left hand is generally employed in lifting the clothes, while the right is armed with a boot-jack, or stout shoe, or some other convenient weapon, with which the Scorpion may be immolated to the just wrath of its discoverer, before it can run off and hide itself afresh. Shoes, boots, and gloves are also favourite resorts of the Scorpion, which has caused many an inexperienced traveller to buy future caution at rather a dear rate.

Scorpions may be found everywhere, under every stone, and in every crevice; and it not unfrequently happens that when a