158 
EDIBLE BRITISH MOLLUSKS. 
and appear likely to continue so. Some thouglit that 
by means of its foot it perforated the soft clay or stone 
which hardened round it; and a Dutch philosopher 
named Sellius, nearly 130 years ago^ published an ac- 
count of the Teredo, wherein he showed that its shell 
could not be the instrument of perforation ; and asked 
how it was possible that the extremely tender shell of 
the young Teredo could make a hole in solid oak — a 
material ten times harder than itself. He also observed 
that the form of the tube is evidently not the result of 
an auger-like instrument, because it is broader at the 
bottom than at the top and sides. 
Mr. Jeffreys, who quotes the above in his ^ British 
Conchology,’ agrees with Sellius that the foot or mus- 
cular disk and not the shell is the sole instrument of 
perforation by the mollusca of stone, wood, and other 
substances, which is closely applied to the concave end 
of the hole, and is constantly supplied with moisture 
through the glandular tissues of the body.^’ He adds, 
By this simple, yet gradual process, the fibres of wood 
or grains of sand-stone may easily be detached or disin- 
tegrated, time and patience being allowed for the opera- 
tion.^^ Some naturalists believe that it is accomplished 
by means of an acid contained in the fish, by which it 
dissolves the calcareous rocks; while others maintain 
that the Pholas bores by using its shell as a rasp. This 
mechanical process is fully described by “ Astur,^^ who, 
from his own observations, has endeavoured to solve the 
problem, and who, to quote Mr. Buckland^s words, is 
apparently the only person who has ever seen the 
Pholas at work.” In the ‘ Field, ^ “ Astur^^ published 
some time since an interesting description of the me- 
thod by which this mollusk bores its habitation. He 
