ON ACEPHALA. 409 
sess the property of shedding a phosphoric light, appears in- 
clined to believe that the fluid which serves the lithophagous 
mollusca to soften and dissolve the calcareous stone in which 
they lodge, contains a greater or less quantity of phosphoric 
acid. Whatever probability may attach to this view of the 
subject, it is far from being beyond the reach of doubt, the 
more so, as it would seem, from Spallanzani, that pholades 
are also lodged in rocks which are not calcareous, as, for in- 
stance, in lava. A chemical analysis of this black liquor of 
the pholades would be highly desirable, to ascertain whether 
itis acid or not. That it is so, is not very probable, as the 
patella, which excavate pretty deeply the calcareous stone 
of the coasts of the Channel, where they live, have no trace of 
acid in the humour which issues from their foot; so that it 
appears a tenable opinion, that the excavations, more or less 
deep, formed by the mollusca in stones, are owing to a simple, 
constant maceration, produced by the mucous fluid which 
issues from the foot. It is probable that it is the same way 
with worms, which possess the same faculty; for though, un- 
fortunately, we are as yet but very insufficiently acquainted 
with them, we may nevertheless presume that their mouth 
is not armed with organs or instruments by means of which 
they could act mechanically upon the stone; were it so, they 
would be no longer worms properly so called, but species of 
the family of the mereides, and the problem would be less 
difficult to solve. 
The pholades present another singularity still more inex- 
plicable than their mode of lodging in the stone. This is 
their phosphorescence. It appears that there are few mol- 
lusca which are so luminous; and it is said that persons who 
eat them raw, and in an obscure or dark place, seem to be 
swallowing phosphorus. No one appears to have attempted 
any explanation of this phenomenon. The pholades feed, 
probably, like others of the family, on small animals, which 
