144 MARVELS OF FISH LIFE 
flat upper valve. These included several molluscs, and 
the feathery growths well shown in the photograph, 
the latter being colonies of hydroids, which, had they 
been undisturbed, would have given birth to many 
thousands of jelly fish. 
After a time the scallop slowly opened, as shown 
in the illustration. This is the position in which he 
lies on the sea bottom, and as the water passes between 
his valves, he extracts from it the numerous forms of 
minute life upon which he exists. The fringes all round 
the top and bottom valves are parts of the mantles ; 
the space between the mantles and the internal organs 
in bivalves is known as the mantle-cavity, and in this 
mantle-ecavity are the gills. As the scallop les on the 
bottom, a hungry crab may attempt to introduce his 
claws between the valves in order to pull out a dainty 
meal, or the shadow of a skate may pass over him. In 
either case the valves would instantly close with a 
snap. How is it that the scallop is able to detect 
these enemies, and how does he shut up so rapidly in 
order to defend himself from attack ? 
It will be seen that the free edges of the mantles 
are prolonged into delicate sensory tentacles, and these 
feel the touch of the crab’s claw in the darkest depths. 
These tentacles also prevent unsuitable matter from 
passing in between the valves, for should anything 
come up against them, the valves partially close with a 
little jerk, and shoot out a stream of water which, 
causing a current, washes the undesirable matter away. 
