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 mud 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 1 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 1 was much surprised at the 
absence of the worms from the dead shells; hut 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 sullicient shell to 
force the entrance of the worm-tube away 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 
few 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 number 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 effort 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 
