46 
old-established cases that grooves and tubular openings are found, 
and there they only exist on the margins as a rule. The above 
remarks apply to the old or thick parts of the valves ; the newer 
thin deposit over the mud, as before mentioned, merely exhibits 
the irregularities of the surface over which it was laid whilst in a 
soft pliable condition, and is usually without any trace of grooves, 
except near the margin. Even these grooves, when examined with 
a lens, show a mould of what was beneath, without exhibiting 
any signs of having been bored. Another feature is the entire 
cavity occupied by the mud and worm, which cannot be accounted 
for by the boring theory. If the worm bores into the substance 
of the shell, how are the blister-like cavities formed ? It is not 
reasonable to suppose that the worm has the power of raising a 
rigid layer of shelly matter and forming a blister. To do this 
the layer must be rendered pliable, otherwise there would be 
evidence of such raising in the shape of cracks, etc. If the 
blisters are formed by the disintegration of the shell, there ought 
to be some evidence on the inner surfaces ; but there is nothing 
to show that disintegration had taken place. One surface is 
comparatively smooth, and the other a perfect mould of the 
enclosed mud. 
Is it not more reasonable to suppose that the upper layer 
is deposited over the mud whilst in a soft state, simply covering 
the mud and worms, than to suppose that the worm bores into 
the shell and then forms the blister 1 If the blisters were formed 
by the disintegration of the shell, there ought to be some variation 
in the thickness of the layer, inasmuch as the disintegration would 
be unequal, and be most evident immediately over the worm. 
Such, however, is not the case; the deposited layer is pretty 
uniform in thickness over each blister. 
From an examination of a large number of shells in sections, 
it appears to me that the cavities when once formed are never 
enlarged in any perceptible degree. Frequently, when viewed in 
section, cavities may be seen one above another in tiers, each one 
distinct, but regulated in form by the one below. These various 
cavities simply represent the entrance of so many worms into the 
open shell at different times, each worm in turn being covered 
over by a thin deposit. 
Mr. A. Oliver, in an article in the “ Centennial Magazine ” for 
September, 1889, suggests that the death of the oyster takes place 
from being unable to close the valves on account of the under- 
mining of the attachment of the abductor muscle. I may say 
that during the whole of my investigations I never met with such 
a case, a fact which militates against the boring view. I, how- 
ever, met with many instances in which the muscular spot was 
considerably lessened, not by its being undermined, but by the 
encroachment of the worm around the point of muscular attach- 
