This animal having selected a piece of floating wood for its permanent abode, attaches itself to it by the head, which is immovably fixed by a tenacious glue exuded from glands at the base of the antennæ. The bivalve shell is subsequently thrown off, a portion of the head becomes excessively elongated to form the peduncle of the Barnacle or Lepas, and in that state it is exactly like the Lucifer Stomapod. In the Balanus, on the contrary, the head expands into a broad disk of adhesion, and the animal resembles the Mysis or Opossum Shrimp. From the first segment of the throat a prolongation is sent backwards which covers the whole body, and the outer layer is converted into the multivalve shell; and the three pairs of cirrhated feet, which were formed in the larval state, now bend backwards from the other three rings of the throat. Though the Cirripeds lose their eyes in their mature state, they are sensitive to light. They draw in their cirrhated feet, and the Balanus even closes the lid of its shell under the shadow of a passing cloud. SECTION IX. BRYOZOA, OR POLYZOA. A BRYOZOON is a microscopic polype, inclosed in an open horny or calcareous sheath, out of which it can protrude and draw in the anterior part of its body. It is seldom or never seen alone, on account of its tendency to propagate by budding. When the buds spring from the sides of the sheath or cell, it is known as the Sea Mat, or Flustra. The Flustra, which is common on our coasts, spreads its hexagonal cells like a delicate network over sea-weeds, shells and other marine substances. Sometimes the polypes are so closely arranged on both sides of a leaf that a square inch may contain 1,800. In the calcareous genera, Eschara and Cellipora, the cells have a lid movable by two muscles, so that the polypes can close the orifice, and shut themselves in.