42 
tained of the habits of the worm, it appears that a large amount 
of mud is necessary to its existence, and that the more muddy 
the place, the better the worm thrives ; such being the case, it is 
reasonable to suppose that those oysters which are fixed on some 
solid body, and somewhat above the surface of the mud, will 
have a better chance of escaping the ravages of the worm, than 
those which are partially buried in mud or lying loose on the 
surface. I conclude, therefore, that if some loose material, such 
as stones, old shells, &c., was placed on the mud-flats for the spat 
to set upon, removing it from direct contact with the mud, that 
the prevalence of the worm would be considerably diminished. 
In the absence of such material, the worms have no other alter- 
native but to fix on the oysters as a place of refuge. 
Symptoms of the Disease. 
Oysters which are badly infested with worms may be detected at 
a glance by their thick rounded outline, and the absence of thin 
sharp edges. Moreover, by looking along the anterior margins of 
the valves, the entrances to the worm tubes will, on close in- 
spection, be readily seen ; those openings furthest removed from 
the edges of the shell having a keyhole-like outline^ whilst those 
on the actual margins are semicircular . In the majority of cases 
the worms are found on the anterior margins of both the upper 
and lower valves, and frequently on the posterior margins, but 
rarely on other parts. On opening the diseased oyster, the valves 
will be seen to possess a series of blister-like structures, which are 
very variable in shape and extent, usually they are more evident 
on the lower valve than on the upper. On pressing the surface 
of these blisters with the point of a knife, it readily yields, and 
underneath will be seen a quantity of light brown mud in which 
the worms are embedded. Each worm has its own collection of 
mud, and from it a membranous tube often extends a short dis- 
tance beyond the edge of the shell. The tube is invariably 
curved, but it is usually curved in such a way that the entrance 
and the outlet are in close proximity to each other, the inlet and 
outlet being often inclosed by the thin layer of shell deposited by 
the oyster. When viewed in section the opening of the tube is 
semicircular, the older part of the shell forming the base, and the 
newer layer the half-circle ; or there are two openings, each con- 
sisting of three-fourths of a circle, with a space connecting them 
together, and bounded above and below by linear layers of shell. 
On removing the thin shelly matter it will be seen that the inner 
surface retains all the inequalities of the mud over which it was 
deposited, and forms a sort of mould of the inclosed mud, and 
rarely exhibits any distinct groove except near the edge. The 
older parts of the valves upon which the worm rests, exhibit 
grooves of certain depths, varying according to the length of 
