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CLASS IV. ANNELIDA.* 



. THIS Class, of which the Earth-worm forms a 

 familiar example, is distinguished by the possession 

 of red blood, which circulates in a double system 

 of arteries and veins. The form is always length- 

 ened, and composed of a great number of rings, 

 generally much alike in appearance. There are no 

 limbs properly so called, but in most cases, each 

 ring is provided with a set of stiff bristles, setce, 

 which assist the animal's motions. The head is 

 often furnished with fleshy tentacles, varying in 

 shape, which are probably organs of touch : and 

 some appear to have little black eyes. The mouth, 

 in some cases, is armed with formidable jaws, but in 

 others consists of a simple tube. They breathe for 

 the most part by means of gills, which appear exter- 

 nally, in the form of little tufts beautifully branched, 

 attached either to the front or to the middle of the 

 body : but some breathe, either by means of the 

 whole surface of the skin, or by little cavities in the 

 body. With the exception of the Earth-worms, all 

 the species inhabit the waters. There are three 

 Orders. 



* A nnellus, a little ring. 



R2 



