238 



ZOOLOGY. 



to Olymene, having been dredged by the Challenger Expedi- 

 tion at the enormous depth of over three miles (about 5000 

 metres). 



Class X.— ANNULATA. 



Body long, Klaierally symmetrical, cylindrical, consisting of numerous 

 segments, either unarmed, or more usually provided with setm alone or with 

 setas and paddle-like appendages {rami). Head simple, with a few simple 

 eyes, or "provided loith tentacles {antemim) alone, or with tentaclesand bran- 

 cMce. Aneversiblepharynx,armedu)ithteeth, usually present. Alimentary 

 system straight, the tubular stomach sometimes sacculated; vent always 

 situated in the last segment of the body. Nervous system well developed, 

 consisting of a brain and ventral ganglionated cord. Circulatoi'y system 

 closed, with a dorsal and ventral and lateral vessels connected by anasto- 

 mosing branches in nearly each segment. A system of numerous paired 

 segmental organs. Sexes united or separate. Embryo passing through 

 a cleavage-stage {morula or blastula), gastrula, sometimes a neurula stage, 

 and after hatching, development is either direct or there is a marked met- 

 amotphosis, the larva passing through a troehosphere and cephalula 



Order 1. Sirudinea. — Body unarmed, finely segmented ; with a poe- 

 terior sucker. (Hirudo, Nephelis.) 



Order 2. Annelides. — Suborder 1. 0%0(;A(i?to (Lumbricus, Nais). Sub- 

 order 2. — Chcetopocla (Arenicola, Syllis, Autolycus, Apliro- 

 dite, Polynoe, Amphitrite, Terebrella, Sabella, Serpula, 

 Spirorbis). 



Tabular View op the Classes of Worms (Vermes). 

 Annulata. 



Brachiopoda. 



Polyzoa. 



Enteropneusta. 



Tunicaia. 



Qephyrea. 



Nemertina. 



I 



Rotatoria. 

 I 



Nematelminthes. 



Platyhelminthes. 



I 



Vermes. 



