176 



ZOOLOGY. 



to Clymene, having been dredged by the Challenger Expedi- 

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

 metres). 



CLASS IX. ANNULATA. 



Body long, bilaterally symmetrical, cylindrical, consisting of numerous 

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

 setae and paddle like appendages (rami). Head simple, 'with a few simple 

 eyes, or provided with tentacles (antennas,) alone, or with tentacles and bran- 

 chiae. An eversible pharynx, armed with teeth, 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. Circulatory 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 pasting through 

 a cleavage-stage (morula or blastula), gastrula, sometimes a neurula stagt\ 

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

 amorphosis, the larva passing through a trochosphere and cephalula 



Order 1. Hirudinea. Body unarmed, finely segmented ; with a pos- 

 terior sucker. (Hirudo, Nephelis.) 



Order 2. Annelides. Suborder 1. Oligochceta (Lumbricus, Nais). Sub- 

 order 2.Chcetopoda (Arenicola, Syllis, Autolytus, Aphro- 

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

 Spirorbis). 



TABTILAK VIEW OF THE CLASSES OF WOKMS (VERMES). 

 Annulata. 



VERMES. 



