188 THE WORLD OF THE SEA. 
Limas leap in their watery element like the butterflies in the air. 
This motion is aided by long, slender, cylindrical, and very con- 
tractile tentacles, which are attached to the fringe of the mantle. 
They are composed of a number of little ring-joints, which can, 
if necessary, pass one within the other, after the fashion of a 
pocket-telescope. 
The Razor-shells, or Solens, force themselves vertically some 
depth into the sand. The place where they are buried is indicated 
A PHOLAS IN A PIECE OF STONE. 
(Pholas dactylus.) 
by a hole in the sand which corresponds to the siphon of the 
animal; when the mollusk is alarmed, it squirts up this hole a 
jet of watery liquid. It entombs itself with a foot of unusual 
dimensions, a natural dirk, with whose pointed end it readily 
excavates a hole; this it soon renders cylindrical, and then draws 
in the shell. In a very little time the razor-shell can bury itself 
fifteen or twenty inches deep. 
The Pholade@ are a family which can bore out for themselves 
a residence in wood or even stone. They appear to carry with 
them a graving tool, and the shell is fitted in a hole as in a 
needle-case. How can these animals bore their way into the 
very hardest rocks? Aldrovand believes that they were born in 
the bosom of the rock while it was in a soft state, and Réaumur 
