47 



ment and deposits of shelly matter all round, so that the spot, 

 after the removal of the muscle, appeared to be in a deep hole 

 owing to fresh deposits being laid down all around it. 



The death of the oyster is brought about chiefly by the 

 decomposition of the nnid after the death of the worms ; but no 

 doubt the imperfect closing of the valves has its effect. In all 

 cases in which the worms are numerous, the edges of the valves 

 are defective, from the fact that the worms occupy the edge and 

 that the shelly deposits are used in lining the shell. Oysters 

 that are infested with worms are much more sensitive than those 

 which are free from them — at least those which I kept under 

 observation were so. If the vessel containing them was dis- 

 turbed, the diseased oysters were the first to close and the last to 

 open. This sensitiveness will tend to deprive them of a large 

 quantity of food. In addition there are the worms placed in the 

 current which carries the food to the oyster, and which in bad 

 cases may number from twenty to thirty, each feeding on the food 

 drawn from the supply of the oyster. 



During my stay at Newcastle I was much surprised at the 

 absence of the worms from the dead shells ; but after keeping 

 some oysters under observation for about six weeks, I began to 

 see the reason for this. The fact is the worm is a sort of com- 

 mensal and partly parasitic on the oyster, in so far that it only 

 appears to thrive when in the currents of water created by the 

 oyster. If the oyster can succeed in forming sufficient shell to 

 force the entrance of the worm-tube aw^ay from the edge, so that 

 the opening is out of the current, the worm appears to leave the 

 shell. I opened some badly infested shells, took out the oysters, 

 and then replaced the valves in the water. In the course of a 

 fevv days the worms deserted the valves, which to my mind tends 

 to prove that unless they are in such a position as to partake of 

 the food drawn in the current by the oyster, they leave their 

 position and seek some other abode. During my observations I 

 never saw the adult worms attempt to obtain an entrance into a 

 fresh oyster. I selected a young oyster and placed it in a vessel 

 by itself. With it I repeatedly placed a numljcr of adult worms, 

 with a view to determine if they would attack the oyster ; but in 

 all cases the worms appeared quite incapable of getting into the 

 shell, and they invariably died within a very short time. They 

 seemed to make no elibrt to gain an entry into the oyster, 

 although placed near the edge of the shell and often on the 

 surface. They rolled about in a very helpless sort of way, 

 collecting small particles of floculent matter around them for 

 concealment. 



Evidence as to Boring, from an examination of the Shell. 



One frequent appearance of the interior of the valves tells 

 very forcibly against the boring theory. In many cases the worm 



