WORMS 171 



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 analo- 

 gies 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, swal- 

 lowing sand and mud for the sake of the organisms they con- 

 tain. They themselves are food for fishes, which devour them 

 in vast quantities, rooting them out of their burrows or cap- 

 turing them at night, at which time they swim about. 



CLASS CHJETOPODA 



C" Bristle-footed ") 



The bristle- worms. This class of worms has bunches of bristles 

 on both sides of each segment of the body, which serve as organs 

 of locomotion, or bristle-feet. 

 The bristles emanate from 

 outgrowths of the body 

 known as parapodia, which 

 are practically limbs. The 

 parapodia are sometimes 

 divided into distinct lobes 

 or branches. The bristles 

 are of various shapes and 

 of ten of brilliant color. They wnt.cirr * s 



* A magnified parapodium of Nereis dumerilii: dors. 



are USUally horny, SOmetimeS <^-. dorsal cirrus ; vent, cirr., ventral cirrus ; s, setw. 



simple, sometimes divided into joints, and vary in shape in different 

 genera.. The parapodia have, besides the bristles, a second set of 



