Page:Popular Science Monthly Volume 13.djvu/565

Rh 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,