SALT AND FRESH-WATER CLAMS. 23 
blackened tube, improperly called the “head,” gradually pro- 
trudes beyond the margins of the shell. Slowly extending, it 
attains the length of three or four inches, and now we notice 
that this organ has two openings at the end, beautifully 
fringed with appendages like little feelers, and mottled with 
the richest brown. And this tube, then, is really a double 
tube leading to the body of the clam. Notice carefully the 
opening and you will see a current of water pouring in at 
one of them, and as steadily flowing out of the other. These 
currents are produced by the tremulous motion of innumer- 
able minute hairs, or cilia, which line the interior of the 
animal. 
The clam has no power to seek its food, being confined to 
its burrow in the sand or mud. Its food consists of minute 
particles of organic matter floating in the water, and thus it 
is through the medium of the ingoing current of water, that 
nourishment is carried to it. While the water conveys food 
to the mouth, it is also charged with oxygen to revivify the 
blood; for the clam has blood, and a heart, and vessels to 
circulate it. What admirable uses do we see already in the 
so-called head of the clam. Lying buried as it is to a con- 
siderable depth in the mud, these tubes are thrust to the 
surface to conduct the pure water laden with nourishment for 
the stomach and gills. The water, as it passes out through 
the other tube, carries with it all excrementitious matter and 
other waste from the body. 
: In the “Annals and Magazine of Natural History,” Messrs. 
Alder and Hancock describe the appearance of these cur- 
rents. From their account we extract the following: “We 
lately have had an opportunity of observing Mya arenaria in 
its native haunts, and watched the play of its siphonal cur- . 
rents under very favorable circumstances. This species, at 
the mouth of the Tyne, buries itself to a depth of six or 
eight inches in a stiffish clay, mixed with shingle; and in 
shallow pools left by the tide the tubes may be seen just 
level with the surface of the muddy bottom in full action. 
