most favourable spot by the current of water drawn in by the 
oyster. If so, then we have the explanation why it is that 
the anterior margin is more often infested than any other part of 
the shell. The worms appear to have the power of collecting a 
large quantity of mud in a very short time. Some which I kept 
in confinement in moderately clear water added fully one-quarter 
of an inch to the length of their tubes in about an hour, and I 
have frequently removed the projecting tubes at night, and in the 
morning they liad been repaired and projected beyond the edges 
of the shell fully half an inch ; so that a vigorous young worm 
on entering an oyster can soon accumulate a large quantity of 
mud, which is immediately covered over by the oyster with a thin 
layer of shelly matter, and if the oyster is healthy, the deposit 
is laid down quickly, confining the worm with its patch of mud 
to a very small space. On the other hand, if the oyster is 
unhealthy and already infested, the shelly deposition is slower 
and the worm collects a large patch of mud before the layer is 
solidified. Hence it is that the size of these accumulations of 
mud get larger as the worms increase and the oyster gets weaker. 
In some very severe cases the whole of the lower valves were 
covered with freshly collected mud, and the oysters were reduced 
to a mere skin, and utterly incapable of secreting any shelly 
matter. The efiect of these blister-like structures, which increase 
in number and size as the disease progresses, is to practically fill 
up the whole of the lower valve and to bulge out the upper, so 
that there is no room left for the oyster. 
In all cases the recently collected mud is of a light brown 
colour, and was found to be the work of young worms varying in 
length from one-eighth to half an inch, the patches of mud 
tin the larger examples varying from one to one and a half inch in 
length, by one-half to three-quarters of an inch wide. I n most of 
the examples mentioned the surface of the mud was covered by a 
thin pliable membrane. The mud surrounding the adult worm 
is usually more compact and darker in tint, often inclining 
to slate colour* whilst the mud which the worms have left is 
frequently black. No doubt it is partly due to the decomposition 
of this black mud that so many oysters die. The parts of the 
oysters overlying these putrefying patches are always discoloured 
by yellowish spots. 
When the habits of the young worm arc considered in con- 
nection with the evidence derived from the examination of oysters, 
in which the worm has just established itself, it points to the 
conclusion that the larvte simply swim into the open shell ; and 
there is no evidence of any boring having taken place from 
without from the fact that the place occupied by the worm is 
quite smooth, and even in those cases in which the worm is full 
grown, the surface is often devoid of any grooves. It is only in 
