14 A STRANGE TENANT. 
under the shell of the fissurella; and, thanking 
his lucky stars for such a fortunate deliverance, 
wished to make the best of his liberty, and rejoin 
his friends. But in displacing other shells, I 
found in nearly every one a similar tenant: the 
secret was discovered—the worm was a parasite, 
that lived in peace and good-fellowship with the 
Keyhole, recalling to my remembrance Oppian’s 
lines on the pinna and the parasitic crab— 
One room contains them, and the partners dwell 
Beneath the convex of one sloping shell, 
Deep in the watery wastes the comrades rove, 
And mutual interest binds their mutual love. 
That the parasite worm does no harm is clearly 
proved by the healthy state of the mollusc in 
whose shell it takes up its abode. How far 
mutual interest may conduce to mutual friend- 
ship, I am unable to say. 
On more carefully examining the position of 
the worm, I found it was invariably coiled away 
in a semicircle under the foot, like a ribbon on 
its edge, never flat. This seems to me a wise 
' provision; for the pressure of the muscles when 
the limpet grips the rock would crush a soft- 
bodied worm to death, if flat; but by being edge 
on, which is the position chosen, all risk of harm 
is avoided, as it fits in a cleft between two layers 
of soft material. 
