ANNELIDA (SEGMENTED WORMS). 



The earthworm may be taken as a representative of this 

 group, the members of which have a marked external seg- 

 mentation of the body, but which lack jointed appendages. 

 They also have a dorsal brain and a ventral ganglionic 

 nerve-cord; the ganglia, like all other parts, being segment- 

 ally arranged. There are nephridia in each segment, while 

 the circulatory system consists of a dorsal vessel in which 

 the blood goes forward, a ventral vessel in which the flow 

 is towards the tail, and segmen tally arranged transverse 

 vessels which connect the two. The annelids are divisible 

 into several groups or orders, only two of which need be* 

 mentioned here. 



ORDER I. CH^ETOPODA. 



In these the body-cavity is well marked, as in the earth- 

 worm ; and each segment of the body bears setae, which 

 serve as locomotor organs. In some (OLIGOCH^ET^:) the 

 bristles are comparatively few, and they arise directly from 

 the body-wall, while appendages of all kinds are lacking. 

 A few of the Oligochsetes live in the sea ; more occur in 

 fresh water, but the great majority are terrestrial, and are 

 familiarly known as "earthworms" or " angleworms," 

 the latter name being given from their use in baiting fish- 

 hooks. The earthworms burrow in the soil, feeding upon 

 decaying vegetable matter in the earth. They swallow 

 earth and all, and come to the surface to deposit their well- 



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