SECTION X 

 PHYLUM ANNULATA 



THE phylum Annulata comprises four classes of Worms the 

 Chcctopoda or Earthworms and marine Annelids, the Archi-annelida, 

 the Gephyrea, and the Hirudinea or Leeches. All of these, except 

 the Gephyrea, have the elongated body divided externally into a 

 number of rings, which represent a division of the internal parts 

 into a series of segments or metameres. There is usually an 

 extensive ccelome, and there is in most a system of blood-vessels. 

 The nervous system consists of a cerebral ganglion, oesophageal 

 connectives, and a double ventral nerve-cord, which in all but the 

 Gephyrea is segmented into a series of ganglia. The organs of 

 excretion are in the form of metamerically arranged pairs of tubes, 

 the nephridia or segmented organs, leading from the coelome to 

 the exterior, and all these, or certain specially modified pairs of 

 them, may have the function of permitting of the passage outwards 

 of the reproductive elements. 



CLASS I. CHJETOPODA. 



The Chaetopoda, comprising the Earthworms, Fresh-water 

 Worms, and Marine Annelids, are Worms the body of which, un- 

 like that of a Flat-worm or a Round-worm, is made up of a series 

 of more or less completely similar segments or inctmncrcs, each 

 containing a chamber or compartment of the body-cavity and a 

 section of the alimentary canal and other organs. At the sides 

 of each are a pair of muscular processes, the parapodift, which do 

 duty as limbs, bearing bundles of seta? or bristles, and bearing also, 

 usually, certain tactile appendages, the cirri. There is an extensive 

 ccelome, incompletely divided into a series of chambers correspond- 

 ing to the segments, by a series of muscular partitions, which act 

 also as mesenteries, being attached internally to the alimentary 

 canal. The latter extends throughout the length of the body : 

 the intestine is usually constricted between the segments. There 



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