52 THE SHELL-FISH OF THE COAST. 
mollusk, and allowing the shells to accumulate on 
these boughs for a period of several years. They 
are then raised, the quantity sold by weight, and 
distributed over the interior of the country. 
The muscle when first hatched is an active 
free-swimming little creature, which attaches itself 
when no larger than the head of a pin. But much 
later in life it still possesses the power of disen- 
gaging the attaching byssus, and securing a new 
anchorage when such is needed. By alternately 
passing forward its delicate threads, the animal 
pulls itself along to a selected locality, much in 
the manner that is adopted by many spiders in 
securing their prey. 
Readily distinguished from the edible muscle by 
its rounded anterior outline and the plications or 
HorRseE-MUSCLE. 
radiating lines extending down _ the sides of the 
shell, is the so-called horse-muscle (Modiola plica- 
tula), like the former an inhabitant of the shallows 
about tide-water. Here, in the somewhat peaty 
soil, they are frequently found burrowing in vast 
numbers, so closely packed together as to form a 
true stratum. The shells are often much eroded 
