332 MUSSEL CLIMBING. 
the dimyaries, or two-muscled bivalves, well represented by 
the common edible mussels, possess a foot, which is not 
greatly unlike that of the snails. The mussel’s foot, how- 
ever, presents in its class, the least developed condition of 
this organ, for it is a spinner, rather than a walker; or, as 
Owen says, "it is subservient to the function of a gland, 
which secretes a glutinous material analogous to silk, the 
filaments of which are termed the byssus,” which often 
serves for attachment to rocks. He farther says, "in most 
dimyary bivalves the foot is an organ of locomotion.” Some 
of the river mussels in babyhood spin a byssus with which 
to moor themselves against the currents of the stream. 
When older grown this necessity is overcome, and the capac- 
ity just mentioned is lost. Then the adult turns its foot 
into a plow-share, and is dragged along in the furrow it 
makes in the mud. The razor-shell alternately bores down- 
wards and propels upward, the foot doing all the work. 
With the foot as an elastic spring the heart-shell leaps along. 
But the common black mussel, Mitylus edulis, and its de- 
spised neighbor, the brown horse mussel, Modiola plicatula, 
who ever saw them walk? Propulsion is not always walk- 
ing. The scallop with its large adductor muscle, by snap- 
ping together its light valves, thus forcibly ejecting the. 
water within against the water without, flits through, and 
sometimes even skips upon its native element, like an aquatic 
butterfly. But no pedestrian does so in all Mollusca-dom. 
Why then should not these pedate bivalves, the mussels, 
walk as others of their own people do? "For want of 
brains!” says one. You are mistaken, sir. They have 
brains, the right kind too, and in the right place, — a real 
pedal nerve-mass, or ganglion; a little bilobed brain at the 
very bese of the “understanding” itself, that is, exactly un- 
der the foot, as was fabled of a very agile dancer, that his 
brains were in his heels. 
Now, if seeing is believing, mussels can walk. We once 
saw a young brown mussel, of the species Modiola plicatula, 
