been remarked that piles placed in dirty, muddy water, near drains, for example, are protected thereby. The water should have, moreover, a certain degree of saltness; the teredo cannot live in brackish water; that is a point to which we shall return later.

The teredo continues to grow in the wood; while the gallery which it forms presents near the surface a diameter of only one-quarter to half a millimetre, it enlarges little by little, until it reaches a diameter of five millimetres and more; as regards his length, and consequently that of the tube which incloses him, we have sometimes found it to be thirty to forty centimetres. He never goes upward more than half-way between the flow and ebb of the tide; although the teredo is thus, for a short time, partially above the water, yet it appears that the wood holds a sufficient amount of moisture to sustain his life temporarily.

The researches of Kater have still further shown, what had already been remarked by Sellius, that the teredo can hibernate in the wood, and that it is those individuals, thus preserved, which in the spring go through with all the phenomena of reproduction-i. e., the formation of eggs, fecundation, development, and expulsion of the young.

The part of the external integuments which constitutes the mantle deposits a calcareous matter, forming an interior lining to the gallery in the wood (Fig. 12, f); between this calcareous casing and the body of the animal there remains a space sufficient to prevent any inconvenience, at least during the act of respiration; for it is possible that when the teredo absorbs water, which serves for respiration, his body is distended, and fills exactly the calcareous tube. The form of this tube, secreted little by little, corresponds exactly with that of the gallery, which has been slowly perforated in the wood; it has the appearance, also, of a series of rings placed one against the other. As the animal progresses, a new ring is added to those which existed before, so that when the tube is closed at its extremity by a calcareous film, its length represents the total length of the animal (Fig. 12, b to c). Among the segments of the tube, those which are nearest the surface of the wood are the oldest and hardest; in the interior of the wood, where the gallery ends (Fig. 12, g), the calcareous ring, newly formed, is at first soft, flexible, and of slight consistency; later, it becomes solid, and closes up the tube, as has been remarked by Sellius. In the variety of teredo described by us, we have never observed the formation of two openings surrounded by calcareous matter, situated side by side, like an eight placed sidewise, ∞,' and serving as a passage for the siphons, as described by Deshayes.

The calcareous tube, once formed, constitutes for each teredo his own abode, where he isolates himself from his companions, and has nothing to fear from their close proximity. One never sees a teredo pierce the tube of another. The tubes make their way side by side, 1 Some Oriental varieties have this form. I have seen them at the Boston Institute of Technology, with solid tubes one and a half inch in diameter.-TRAnslator.

and cross each other in every direction, but, be the wood ever so wormeaten, there always remains a woody wall, often very thin, it is true, between two adjoining tubes.

The very existence of the adult teredos seems dependent upon the wood. Withdrawn from their galleries and placed in sea-water, they could be kept alive by Kater scarcely more than three or four days. Left in the wood, but taken out of sea-water, they would die within twenty-four hours. Deprived at the same time of contact with wood and sea-water, they perished at the end of one or two hours. In damp wood, that is, wood soaked with salt-water, their existence is prolonged somewhat. Wood and sea-water are, then, both necessary. If these two conditions of existence are furnished them, one can, Kater assures us, keep them alive during several months.

The teredo does not always remain in peaceable enjoyment of the home he has constructed, and the nourishment the water brings to him.

FIG. 13.

He finds himself exposed to the attacks of an enemy, of an annelide to which the late M. W. de Haan has given the name of Lycoris fucata (Fig. 13). In our day, as well as at former epochs, this annelide is constantly found wherever the teredo exists. His eggs and embryos are met with in the midst of those of that mollusk.

Kater has remarked that the adult annelide, leaving the muddy bottom, where he has hibernated, and in which the piles are driven, climbs along the surface of the wood toward the opening made by the teredo; there he sucks away the life and substance of his victim; then, slightly enlarging the aperture, he penetrates and lodges in place of the teredo. Later the annelide reappears and seeks for new prey. All the early writers on this subject state that they have found this annelide in wood at the same time with the teredo. It is remarkable that a similar annelide, and perhaps the same, has been found in the cavities hollowed out in stone by the pholades.

It is important that it should be generally understood that this annelide is not only harmless, but renders the greatest service in devouring the wood-destroyer. It is a narrow annelide, ten to fifteen centimetres long, provided on his sides with a great number of small feet terminated with a point and garnished with hairs and showing in front a pair of strong upper jaws, horny and sharp, and lower jaws bent backward in form of hooks and carried outside by the aid of the lower lip, which is developed somewhat like the finger of a glove turned backward. Behind the head are four pairs of tubular-formed gills. With these weapons the annelide pursues and devours the teredo. The observations of Kater teach us that he is generally found in the empty galleries with the remains of the teredo; sometimes even he is seen as if clothed with the integuments of the teredo, while he is occupied in ransacking his intestines. Once Kater had the rare

chance (which, by-the-way, only secures such good fortune to very careful observers) to seize the moment when an annelide, coming out of one of the openings of wood, at once took possession of a teredo that he had placed on the bottom of the vessel which held the wood. He saw the annelide seize the teredo with his jaws, draw him into the canal which he occupied, and devour him so completely that there only remained the two valves of the shell.

It is in an entirely different manner that the cirripeds (Balanus sulcatus) aid in preserving wood. When these animals, to which sailors and the inhabitants of our coasts give the name of Pustules of the Sea, or Sea-Thorns, multiply to such an extent on the surface of wood that their disks touch, without leaving the least vacant space, the natural consequence is, that the young teredo cannot find any place where it can attach itself, and hence it is impossible for him to penetrate the wood. This preservative effect is produced even when the shells have fallen, provided the disks adhere to the wood.

III.

ON THE CIRCUMSTANCES WHICH FAVOR THE RAVAGES OF THE TEREDO.-The commission gave in its first report an historical epitome of the injuries done by the teredo at different epochs in Holland.

When the teredo was remarked for the first time, an idea prevailed that it was imported from abroad; vessels coming from the East Indies were accused of having brought that destructive guest. Two facts show the incorrectness of this idea. On the occasion of the deepening of the Dumbart Dock at Belfast, William Thompson' found, twelve feet below the surface of the earth, in a blue, argillaceous soil, the trunk of a tree entirely riddled by the teredo. Considering the depth at which this débris was found, and the fact that it lay beneath a series of strata of shells, it is certain that it was deposited there ages ago, long before a vessel, coming from the East or West, could touch the coast at Belfast.

Fossil wood, perforated by the teredo, has been found in different localities for example, in the London clay, in the Eocene formations at Brussels, where Van Beneden discovered fossil wood, inclosing the remains of the teredo; and at considerable depth, also, near Ghent, at the time of the construction of the citadel.

The teredo existed in a geological period earlier than our own, and he appears to have been always an inhabitant of our coast. Why is it, then, that at certain epochs, as in the years 1730, 1770, 1827, 1858, and 1859, he multiplied so prodigiously as to destroy entire dikes in a very short space of time? Even as early as 1733, Massuet assigned as a cause an increase of the degree of saltness of the water, resulting

1 W. Thompson, on "The Teredo navalis and Limnoria terebrans," in Edinburgh New Philosophical Journal for January, 1855.

from a diminution in the quantity of the rainfall; the same opinion is found expressed in the reports of many chief engineers of Waterstaat. To decide whether this opinion was well founded, careful analyses were made in 1859, which, compared with those made at other epochs, showed that the proportion of salts found in the water of the Y was just double what was in 1855, and a third more than in 1825.

9

it

The three circumstances, under which this exceptional increase of

U

the teredo was observed, were a moderate rainfall, and, as a direct or remote consequence, a falling of the level of the rivers, and an increase of the saltness of the water of our arms of the sea. As an additional favoring circumstance should also be noted an increase in the temperature.

IV.

EXPERIMENTS IN THE PRESERVATION OF WOOD FROM THE ATTACKS OF THE TEREDO.-To justly appreciate the experiments tried by the commission, it must be borne in mind that when it was discovered, in 1858 and 1859, that great injury was being done to our marine works by the teredo, very many methods of preservation were recommended on all sides to the Government, and that the nature of many of these remedies was kept secret by the persons extolling them. In order that its labors should offer every guarantee of impartiality, and although convinced in advance of the inefficacy of a large number of the means proposed, the commission decided not to lay aside any without a trial. Moreover, as far as possible, it had the pieces of wood to be experimented with prepared by the inventors or proposers of the processes, in order to protect itself from every accusation of unfairness.

FIG. 14.-This cut was made from a Teredo

navalis, taken from a pile exposed two seasons (1876 and 1877) at Horn Island, Gulf of Mexico. When first taken from the wood it was eighteen inches long.

The experiments were made the first year in the ports of Flessingue,

1 Several pages omitted, of no especial interest to American readers, describing local observations of the state of the water and atmosphere, and analyses of the waters, to show their chemical character.

Harlingen, Stavoren, and Nieuwendam, and afterward in the ports of Nieuwe-Diep and Stavoren. The woods employed were oak, red fir, ordinary fir, and Pinus sylvestris, generally in pieces one metre long by two or even three decimetres square. These blocks were prepared in different ways, and care was taken to place by their side blocks of the same kinds of wood without any preparation as counter-proofs.

The trials made by the commission may be placed under three principal groups:

1. Coatings applied to the surface of wood, or modifications of the surface itself.

2. Impregnation of wood with different substances, which modify the interior as well as the surface of the wood.

3. Employment of exotic woods, other than ordinary woods of construction.

COATINGS APPLIED TO THE SURFACE OF WOOD.-The methods belonging to this group, which have been examined by the commission, are the following:

1. Method invented by M. Claasen, and kept secret by the inventor. 2. Metallic paint, invented by M. Claasen and likewise kept secret. 3. Method of M. Brinkerink, consisting of a mixture of Russian talc, coal-tar, resin, sulphur, and finely-powdered glass, applied hot on wood previously roughened by a toothed instrument; this application was two millemetres thick.

4. Method of M. Rijswijk, analogous to the preceding.

5. Paraffine varnish, obtained by the dry distillation of peat, from the factory of MM. Haages & Co., at Amsterdam.

6. Coal-tar, applied cold on the wood in several successive layers, or applied hot on wood whose surface had been previously carbonized. Some pieces were treated as follows: Holes were first bored in them and filled with tar, then plugs were fitted closely to the holes and driven in with sufficient force to make the tar penetrate the wood; other pieces still were painted over with a mixture of tar with sulphuric acid, or sal ammoniac, or turpentine, or linseed-oil.

7. Painting with colors mixed with turpentine and linseed-oilamong others with chrome-green or with verdigris.

8. Singeing or superficial carbonization of the wood.

The pieces of wood thus prepared were placed in the water at the end of May, 1859, and the first examination, made toward the end of September of the same year, showed that neither of these methods afforded any protection from destruction by the teredo. There was one partial exception, and that was the pieces of wood treated according to No. 6; these showed only traces of the teredo here and there. But, at a later examination, in the autumn of 1860, when the wood had been exposed a year and a half, these were also found to be equally severely attacked by the teredo.

The results of these experiments strongly convinced the commission