128 INVEKTEBKATE ANIMALS. 



place of the ]iroper vascular system, and which are known as the 

 " pseudohfemal " vessels. 



The two principal groups included in this division of Annnlose 

 animals are the Gepliijrea (Sjioon- worms) and the Annelida (Ringed 

 W(_irms). 



Cl.VSS I. GEPiIVRE.\. 



This is a small group, incluiling a numljer of worm-like animals, 

 commonly called Spoon-worms, which in man}' resjiects lesemble 

 the Annelides, and have at the same time certain relationships with 

 the Holothurians among the Echinodernis. They differ from the 

 Annelides in not having the body definitely segmented, though the 

 skin is annnlated (fig. 80), and also in the fact that the ventral 

 nerve-chain is not gangliated. Tliere are no lateral appendages, 

 except occasionally bristles. They differ from the Holothurians in 

 the want of an ambulacral system and the non-radiate character of 

 the nervous system. The Spoon-worms are all marine, and the most 

 widel)' distributed genus is Sipvnciilns (fig. 80), which ranges from 

 between title-marks down to a depth of 2.500 fathoms. 



(Jla.ss II. Annelida. 



The Annelida or ^lji«!(to(./, commonlj' known as Ringed "Worm.s, 

 are distinguished l^y the possession of definite segmentation, the 

 body being composed of a number of rings wliich are all similar to 

 each other e.xcejit at tlie two enils of the hoAy. All the Annelida 

 are moi'e or less worm-like in shape, and in all except the Leeches, 

 the segments are (some or all) ])rovided with lateral appendages 

 which mostly subserve locomotion, but which are never jninted to 

 the liody. In the tyjiical Annelida each .segment (tig. 81) consists of 

 two arches, termeil, froni their jKwition, resjiectively the "dorsal 

 arc" (rf), and the " ventral /irc" (c). Each segment carries a lateral 

 process on each side, which arc known as the "foot-tubercles" 

 (pariijxidia). Each foot-tuliercle in turn may consist of an n]iper 

 |iiece nr " doi'sal oar"((^), a]id a lower jjiece or " voitral oar " (/)\ 

 both c.-in-ying a tuft of bristles and a. soft juintcil lilament (tlic 

 " cirrus ''). 



The nervous system consists essentially of a double gangliated 

 chain jilaced along the ventral surface of the body, and traversed in 

 front by the gullet, sn tli.-it the first jiair of g,-iuglia. lie above the 

 gullet. The digestive systi'm consists iif .a ninulli, geuei'ally with a 

 ]troti-usil)le ]irobosris, ami sometimes luirny j.iws, a, gidlct, stomach, 

 intestine, .-md a, distinct anus. yVs a rule, the .alimentary canal runs 

 str.iight from one end of the body to the other without describing 



