In an allied family and genus (Trichina) is placed one of the most dangerous of human parasites, the _Trichina spiralis_. Here, too, comes that "hairworm" (Gordius), which most country folks call "hair eel" or "hair snake." Many assert with the most positive faith that if you will soak a horsehair in water it will "turn into a snake," and will show you this long threadworm in a horse trough to prove it. I never knew a cautiously made experiment in that direction to succeed; nevertheless the fanciful error survives. The gordius, which does look like a hair from a gray mare's tail, is somewhat aquatic in its habits. CHAPTER VII DWELLERS BETWEEN TIDE MARKS THE COLONIAL MOSS ANIMALS Seaweeds and rocks at and below the limit of the ebbing tide are often covered with small bushy growths, or with lacelike incrustations that are alive. These are moss animals, representing the class Polyzoa of the phylum Molluscoida. They are minute, soft creatures that live in colonies formed by the repeated budding of the members, all connected by a fleshy base so that each contributes to the nourishment of all. "Each little animal occupies a separate stony or horny capsule, into which it may withdraw and even close the opening with a lid.... The mouth is surrounded by tentacles that in many species arise from a horseshoe-shaped or disklike base. These tentacles are always beset with hairlike bristles which by their movements serve to set up currents, and thus to drive minute organisms into the mouth." A typical example of these polyzoans (or bryozoans) is _Bugula turrita_, so abundant wherever our northeastern coast is rocky that the rocks below tide level appear covered with its mossy tufts, which are often ten inches long and profusely branched. The main stems are orange-yellow, while the terminal branches are yellowish white. The delicate tracery so frequently seen on the fronds of kelp, and on shells and stones along both shores of the Atlantic indicate colonies, or their remains, of the lace coralline (Membranipora); and the dull red or pinkish crust so common on shells and stones in shaded tidepools represents successive colonies of the "red-crust" polyzoan (_Escharella variabilis_), layer crusting over layer. A similar history accounts for the curious nodules called "false coral" so common in moderately deep water in Long Island Sound. Similar polyzoans, which exist in great variety, both modern and fossil, contributed extensively to the formation of the older strata of sedimentary limestones. ANCIENT LAMP SHELLS Associated in structure with these minute colonists is the ancient race of brachiopods (Brachiopoda, "arm-footed") or lamp shells, although they much more nearly resemble bivalved mollusks, whence, by the way, comes the name of the phylum to which both belong--Molluscoida, which means "mollusklike."