GENUS ^Cerebratulus^ ^C. angulatus.^ Olive-green, with light dorsal stripe. GENUS ^Cosmocephala^ ^C. ochracea.^ Two to three inches long when extended; gray or yellowish-white, and mottled by the internal organs showing through the translucent body; line of lighter color down the back; anterior end often orange-colored. It is common near low-water mark under stones and in the dead tubes of /Serpula/. GENUS ^Polina^ ^P. glutinosa.^ One to two inches long; color orange or light yellow, with a faint line of deeper color down the center of the dorsal surface; very slimy; eyes numerous, in oblique lines on the head. Found in tide-pools on algæ. PHYLUM =NEMATHELMINTHES= ROUNDWORMS The worms of this phylum have the general name of roundworms, which distinguishes them from the flatworms of the preceding division and from the segmented worms of the /Annulata/. The body is elongated, cylindrical, smooth, and pointed at both ends. With few exceptions, they are parasitic. A few of the nematode species are free, living under stones and among seaweeds at about low-water mark. CLASS =NEMATODA= GENUS ^Pontonema^ ^P. marinum.^ Slender, white, smooth, active, cylindrical; constantly coiling and uncoiling itself. PHYLUM =ANNULATA= SEGMENTED WORMS The name of this phylum expresses the principal characteristic of the group of worms which have elongated bodies composed of series of short parts, or ring-like divisions. Each one of these segments contains a separate and similar set of internal organs. [pg171] The annelids are divided into four classes, one of which, the /Gephyrea/, has not the characteristics which distinguish the group. The classes are easily recognized by conspicuous features. Some have bristles; others have scales; others have tentacles around the head and inclose themselves in tubes. Many are highly colored, and all are of great interest to the naturalist from the diversity of their habits, form, and structure, and from the analogies they bear to other and higher types of animals. The annelids are the highest type of worms, their organs having attained more special functions. The sense-organs of eye and ear are more developed, and the nervous system has distinct centers, or ganglia, the first and largest ganglion being a part of the head. They are found in abundance everywhere. Some species grow to the length of one foot or two feet. Some are carnivorous, others vegetarian, and many are mud-eaters, swallowing sand and mud for the sake of the organisms they contain. They themselves are food for fishes, which devour them in vast quantities, rooting them out of their burrows or capturing them at night, at which time they swim about. CLASS =CHÆTOPODA= ("/Bristle-footed/") [Illustration: A magnified parapodium of /Nereis dumerilii/: /dors. cirr./, dorsal cirrus; /vent. cirr./, ventral cirrus; /s/, setæ.]