368 Mr. Olser on burrowing 
indication of the presence of an acid. The water in which 
a mass of rock, containing above an hundred Saxicavag had 
been kept for a week, afforded a precipitate, when treated with 
oxalic acid, only equal to that obtained from the same quantity 
of common sea-wafer. To explain the failure of these experi- 
ments, it may be observed, that where the Lithophagi happen 
to be lodged in situations which afford them sufficient room 
and shelter, they make no attempt to enlarge their habitation. 
Thus, Saxicava prsecisa is more frequently found among 
groups of Serpulse than in a hole which it has excavated ; and 
I have obtained full grown specimens of Hiatella arctica (Solen 
minutus of Linn.) attached by the byssus to a Pecten. It 
may therefore be presumed that the solvent is secreted only 
when its agency is required ; and this would sufficiently 
explain why a free acid cannot be detected in the animal. 
Litmus, in the smallest quantity, acts as a poison upon them. 
The animals exposed to it remain with their syphons half 
projected, which they do not attempt to retract on being 
touched, and perish in a few hours. If an increased quantity 
of calcareous salts could be detected in water in which they 
had been kept, the experiment would be a decisive one ; but 
when it is considered that the animals live in the open sea, 
and are to be obtained only at low tides, it is not to be ex- 
pected that they will work when confined in a small vessel, 
and deprived of food. 
Had the question been previously balanced, our inability 
to detect a solvent would justify strong doubts of its exist- 
ence : but while all the facts connected with the natural 
history of the Lithophagi afford a strong and consistent sup- 
port to the theory of a solvent, and are opposed as decidedly 
