It is a singular fact that myriads of worms are seen daily, but are not known as such. These are the minute and beautiful Polyzoans (Fig. 66). They are marine animals, grow in colonies, and look like delicate seaweeds. They are often called moss animals. At the seashore we shall find the rocks and particularly the broad fronds of kelp near shore often encrusted with a delicate, beautiful tracery of pure white. In California I have found the kelp leaves at the surface covered with it, having the appearance of being coated with silver. Beneath the glass it develops into a beautiful tracery filled with cells. When magnified these cells are seen to resemble Figure 67, each one having its worm, which seems to blossom like a flower. These worms are minute imitators of corals, as they form a corallike structure, the worms having the faculty of secreting lime, as do the corals, yet they are much higher in the scale of life. One of the common seaweeds of the seashore is the sea mat or Flustra. No one would suspect it of being other than a beautiful marine plant with large leaves or branches, and many a collection of "seaweed," preserved through many years, contains the Flustra arranged among the real "plants" of the sea. But Flustra is merely a colony of worms. The minute spots seen upon it when enlarged beneath a microscope resemble so many cells of carbonate of lime secreted by the worms of the community or colony. Another species of Flustra is shown in Figure 68, and a part of the skeleton of the colony or of each cell is the peculiar bird's head which has a beak. This beak, even after the death of the worm, is seen to open and shut, snapping continually, much quicker than the little pincerlike objects we have seen in the sea urchins. The use of the so-called bird's head is not well understood. [Illustration: FIG. 68.--Bird's-head Flustra: 1, Flustra mat, showing cells; 2, diagram of a single worm (_Polypide_); 3, bird's-head process.] [Illustration: FIG. 69.--Sea mat: 1, sea mat, natural size; 2, 3, section of the animal much enlarged.] [Illustration: FIG. 70.--Lingula.] [Illustration: FIG. 71.--Lamp shells, showing gills.]