BORERS. 
305 
The mode in which the boring Mollusca execute 
their perforations is yet a 
matter of uncertainty. ‘The 
principal hypotheses that 
have been put forth on the 
subject have been already 
briefly enumerated, but it 
may not be amiss to add an 
expression of opinion on 
their value, and a careful 
summing upof the evidence, 
by zoologists eminently 
worthy of deference, theable 
authors of the “‘ British Mol- 
lusea.” 
‘¢ Of all these theories,” 
observe Messrs. Forbes and 
Hanley, “the chemical one, 
so far as a secreted solvent 
is concerned, bears least ex- 
amination in the case of 
the Pholadide. 'The sub- 
stances perforated are wood, 
limestones, hard and soft, 
argillaceous shales, clays, 
sandstone, and (in the case 
of a Pholas, in the mag- 
nificent collection of Mr. 
Cuming) wax. The notion 
of a secreted solvent, that 
would act indifferently on 
all these substances is, at 
present at least, purely hy- 
pothetical ; and, since all 
attempted tests have failed 
x 
PHOLAS. 
to detect an acid, 
