488 On Teredo Navalis, fyc. [May, 



as the interval between them and the sheathing is filled with a layer 

 of cow-hairs. The boards of the sheathing are annually repaired or 

 renewed. Last year it was reported that the sheathing required no 

 renewal, " although" it was thickly covered with muscles. This cir- 

 cumstance reminded me that I earlier had found no Teredines in 

 bulwarks on which muscles (mylilus edidis), were fixed, an observation, 

 which I however had not then followed up. At present I have 

 reason to believe, that the sheathing of the pilot-vessel was not attacked, 

 because it was covered by muscles. As the latter may easily be bred, 

 they offer a natural defence, of no expense, and may besides be turned 

 to economical account. 



The muscle attaches itself to piles by means of the byssus, or fila- 

 ments, and multiplies so readily that its young, if suffered, soon cover 

 the whole surface. In the frith of Apenrade piles have, from time 

 immemorial, been sunk, on purpose for the sake of the muscles, which 

 in the course of four years attain to a length of 3 to 4 inches. They are 

 consumed either in fresh state, or are pickled and exported in large 

 quantities. The smaller muscles are thrown back near the piles to 

 which they soon again attach themselves. The short period in which 

 they will cover a surface, I have had an opportunity of observing, when 

 a new light-vessel was placed near Laessoe in Kattegat. In 6 months 

 her bottom was covered with a thick mass of young muscles, which had 

 tended to impede the speed of the vessel. Two feet square of the 

 mass, submitted to my examination, consisted of several layers of mus- 

 cles, 2 inches in length, so firmly connected by the byssus, that a needle 

 could not pass between them. No single muscle could be detached 

 without the whole mass following. 



Teredo breeds during the dog-days, the muscle some months earlier. 

 Where the latter has fixed itself, the eggs of the Teredo cannot reach 

 the wood, nay, by intercepting the communication with the sea, the 

 muscle will suffocate Teredines, which may happen earlier to have 

 found their way into the wood. 



At first I supposed the byssus might possibly contain something 

 specifically repulsive to the Teredo, and I therefore had it submitted 

 to the chemical analysis of Dr. Scharling, which however has not given 

 the result expected. It is the mere mechanical covering of the muscles, 

 which prevents the Teredo from reaching the wood. 



