PHOLADID.E. 



case, is proved by the immense number, tlie large size, 

 and the depth of tlie perforations etTected by the 

 Pholades, whose shells are still to be found at the 

 bottom of many of the cavities, together with others of 

 existing species, which have concealed themselves in 

 the same liollows. 



Belonging to the same family is the genns Teredo, 

 distinguislied by its elongated, vermiform body ; its 

 thick, eqiiivalve, hingeless shell, which opens at both 

 ends ; and its very delicate mouth, open both in front 

 and at its lower part, so as to admit of the passage of 

 a short foot. The species are numerous, and generally 

 known by the name of S/iiptosrm or Pileicorm, because 

 they perforate and dwell in timber. 



Their burrows take the same direction as the grain 

 of the timber, but if a knot occurs, or the shell of 

 another Teredo lies in the way, they are suitably 

 diverted. The cavity is invariably coated all over 

 with a calcareous incrustation. The Teredo eflects an 

 entrance, in the tirst place, by a very small aperture, 

 and grows within the cavity which it works out. Its 

 growth, however, is very rapid, and the ravages 

 etlected by a number of these animals are almost 

 incredible. We have seen piles so riddled by them 

 as to fall in pieces when handled with any degree of 

 force. A piece of deal lias been found honeycombed 

 by their burrows after an immersion of only forty 

 days. But by a peculiar instinct each Teredo confines 

 itself to its own cavity, and never makes any com- 

 njuiiication with its neighbours. It is by secret 

 iinilermining of this kind that the piles and olher 

 submarine constructions of bridges, and quays, and 

 jiiers are frequently destroyed, and that ships have 

 been silently eaten into, until their timbers have 

 crumbled and sunk under the feet of their crews. As 

 a protection against these dangerous enemies, the 

 bottoms of vessels are now sheathed with copper, or 

 the wood is soaked in some preservative liquid, or 

 diiven full of broad copper headed nails, which serve 

 as a kind of armour. 



M. de Ouatrefages refers to a boat, employed as a 

 p-issage-boat between two villages on the Mediterra- 

 nean coast of Spain, which at the commencement of 

 spring was accidonlally sunk. Four months after- 

 wards she was raised by some fishermen, who hoped 

 to turn her materials to their profit. But in that short 

 period, the Teredos had so perforated and riddled her 

 timber as to render it utterly useless. 



Early in the eighteenth century, half the coast of 

 Holland was menaced with inundation by the destruc- 

 tive labours of the Teredos. They had attacked the 

 piles sustaining the formidable dikes and sea-walls, 

 which the industry of the Dutch had raised to defend 

 tliem against the encroachments of Ocean. To avert 

 ilie threatened peril necessitated a very heavy expen- 

 diture. Fortunately it was discovered, on a close 

 examination of the habits of the mollusc, that it is 

 animated by a singular antipathy to rust, and that, 

 consequently, timber impregnated with oxide of iron 

 is secure against its attacks. It was only necessary, 

 therelore, to soak the timber intended for the repair of 

 the dikes, in a tank of prepared oxide of iron ; in other 

 words, to invest them in a coat of iron rust. 



The Teredo navalU appears to the eye like a long 

 worm without articulations. Between the valves of a 

 little shell, with which the anterior portion is pro- 

 tected, a kind of smooth tvuncature is conspicuous, 

 surrounding the projecting pad or cushion which forms 

 the animal's foot. From this point all iis body is 

 inclosed in the sheath and mantle, forming a sort of 

 sheath which communicates with the exterior through 

 two syphons. 



The mantle is attached to the circumference of Ihe 

 shell. Above, it gathers in two considerable folds 

 which are capable of expansion by the afflux of the 

 blood. The cejihaHc or foremost fold, is of a greyish 

 tint, very light, and tolerably transparent, so that the 

 liver, the ovary, the branchise, and the heart, may be 

 distinguished in the interior, and the pulsations of the 

 latter counted. The syphons are extensible, and 

 attached to one another for about two-thirds of their 

 length, the upper part being longer and thinner than 

 Ihe lower. These tubes admit the water necessary for 

 ihe animal's respiration, and when deprived of its 

 oxygen, discbarge it, and aloi g with it the useless 

 products of digestion. 



On the upper edge of the anterior truncature of the 

 animal's body is the mouth — a flat, and slightly bell ■ 

 shaped aperlure, furnished with four labial palpi, a 

 stomach, and a well-developed intestine. 



The heart consists of two auricles and a ventricle, 

 which beat at irregular intervals, four or five times in 

 the minute. The blood is colourless, transparent, and 

 loaded with small corpuscles of different sizes. The 

 respiratory organs are the branchiiB, or gills, and the 

 mantle ; but one-half of the blood returns to the heart 

 without traversing the branchise. The nervous system 

 is very complete, and includes a brain, nervous fila- 

 ments, the branchiae, the syphon tubes, and certain 

 ganglions distributed tln'ough the mantle. 



The solid mucus, or sheath, inclosing the adult 

 animal is frequently, but erroneously, described as 

 forming part of its body. Shut up in this tube the 

 Teredo is necessarily restricted in its movements, which 

 are simply those of extension and contraction. It 

 neither climbs, nor creeps, nor floats, nor swims, but 

 by alternate expansion and contraction slowly and 

 laboriously impels itself forward. 



It deposits a spherical, greenish-yellow egg, which, 

 soon after fecundation, is transformed into a larva — a 

 larva naked and motionless, but which, after a while, is 

 invested with vibratory ciliae. Then it begins to move, 

 and swim about freely in the water. " When one of 

 these larvte," says a recent writer, "has discovered a 

 piece of submerged wood, without which it probably 

 could not live, the curious spectacle is observed 

 of a being which fabricates step by step, and as it 

 requires them, the organs needful for the due perfor- 

 mance of its functions." The long feet with which it 

 is furnished in its larva state enable it creep along Ihe 

 surface of the timber, until it has found a portion 

 sullieiently soft and porous for its purpose. There it 

 halts, commences the attack, and soon accomp'i-hcs 

 a tiny pore or cell, the entrance to its future burrow. 



" Having thus secured a lodgment, Ihe young Teredo 

 begins to grow ; covers itself with a coaling of mucon.'; 



