321 



PHOLADID^E. 



PHOLADID^. 



322 



increasing in length, closes up the end of its shell, and lives a long 

 time afterwards, furnished with food from the sea-water. Teredo 

 navalii, he observes, closes up its shell in the same manner : it must 

 therefore, after that period, be supplied with food entirely through the 

 medium of sea-water. The Teredines, he adds, turn round in the 

 shell, to which they are not attached, and with which their covering 

 only has a slight connection at one particular spot, to prevent the 

 external tubes from being disturbed. This motion, Sir Everard 

 observes, is for the purpose of boring. 



Some of the Teredines examined by Sir Everard Home were sent 

 from Sheerness in the wood alive, and they lived in salt-water for three 

 days after being brought to town. Sir Everard observed that when 

 the surface of the wood was examined in a good light, while only an 

 inch in depth in the water, the animal threw out sometimes one tube, 

 at others two small tubes. When one only was protruded, the other 

 almost immediately followed it. One of them was about three-quarters 

 of an inch long ; the other only half that size. When the largest was 

 exposed to its full extent, there was a fringe on the inside of its 

 external orifice of about twenty small tentacula, scarcely visible to 

 the naked eye : these were never seen except in that state ; for when 

 the tube was retracted, the end was first drawn in, and so on, until 

 the whole was completely inverted : and therefore in a half-protruded 

 state it appeared to have a blunt termination with a rounded edge. 

 The smaller tube was not inverted when drawn in. " These tubes," 

 says Sir Everard Home in continuation, '' while playing about iu the 

 water appeared at different times to vary in their directions, but usually 

 remained at the greatest convenient distance from each other. The 

 largest was always the most erect, and its orifice the most dilated ; 

 the smaller one was sometimes bent on itself with its point touching 

 the wood. In one instance, where a small insect came across the 

 larger one, the point of the smaller turned round and pushed it off, 

 and then went back to ita original situation. In several instances the 

 smaller one appeared to be the most sensible ; since by touching the 

 larger one gently it did not retract ; but on touching the smaller one 

 they both were instantly drawn in. Indeed whenever they were 

 retracted they always were drawn in together. When the worm was 

 confined within the shell the orifice waa not to be distinguished in 

 the irregular surface of the wood, which wag covered with small fuci. 

 The worm appears commonly to bore in the direction of the grain of 

 the wood, but occasionally it bores across the grain to avoid the track 

 of any of the others ; and in some instances there was only a semi- 

 transparent membrane as a partition between two of them." 



T, naralit has been found at depths ranging from the surface to 

 ten fathoms. 



It is said, probably with truth, that T. navalii was introduced into 

 Europe from warmer climates. However that may be, it now unfor- 

 tunately swarms in our seas. The ravages of this apparently insig- 

 nificant animal are terrible. Ships, piles, all submarine wood-works, 

 are ruinously affected by it : small as it is, it threatened the submersion 

 of Holland by its destruction of the dykes. The living specimens 

 which formed the subject of Sir Everard Home's observations were 

 furnished from one of the royal dockyards. The rapidity of its growth 

 and the destructive celerity with which it works are hardly credible. 

 A piece of deal, after a submersion of forty days, was riddled by 

 them, and some had attained considerable size. Those from the dock- 

 yard at Plymouth, examined by Montagu, were in piles which had 

 been recently taken up to be replaced with new ; they had not, accord- 

 ing to the information given to Montagu, been under water above four 

 or five years, but they were greatly perforated, though they were sound 

 solid oak when they were driven. The only effectual way of pre venting 

 the attacks of this animal upon piles appears to be by covering all 

 that part which is continually beneath the surface with short broad- 

 headed nails. The action of the sea-water on the nails produces a 

 strong coating of rust, said to be superior to a copper sheathing. 



Wood perforated by Tercdiael nmaltl. 



T.gigantea. Rumphius, in his ' Amboiuische Raritiitkammer,' gives 

 two figures, here copied, of a species of tubular shell found in shallow 

 water among mangrove-trees. He describes the ground whence they 

 were brought, and the mode in which the large end of the shell i 

 closed, so an to leave little doubt that it was T. giganlea, though the. 

 separation of the two tubes through which the parts of the anima 

 pass out is different from the specimens brought home by Mr. Griffiths 

 This difference however, as the latter observes, may have been con 



AT. HIST. DIV. VOL. IT. 



iected with the situation in which the animal was found, namely, 

 tiallow water among the mangroves. 



Trredo gigan'ea. (Humph.) 



TtrtAo glgintea. 



1, the small or upper extremity of the shell, the external covering broken 

 away and showing the termination of the tobe>, one of which is broken ; 2, a 

 longitudinal section of that part of the shell where the double tubes are formed ; 

 3, the shell complete, or nearly BO, the exception being the imperfect state of 

 the upper extremity. (' Philosophical Transactions.') 



