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-cavity are the gills. As the scallop lies 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. 



