Private Library of 

 Percy E, Raymond, VERMES. 99 



latter the wheel-animalcules. The Nemathelminthes 

 includes the thread-worms (e.g. Ascaris), only two or three 

 forms are found fossil. 



CLASS. t ANNELIDA. 



The body is segmented and generally the segments 

 are similar. There is a ventral nerve cord and a ring 

 round the oesophagus. A vascular system is generally 

 present. 



There are three orders (1) Chaetopoda, (2) Gephyrea, 

 (3) Hirudinea. 



The Gephyrea includes Sipunculus, Echiurus, etc.; the 

 Hirudinea includes the leeches. Both these orders are 

 represented in the fossil condition by doubtful examples 

 only. 



ORDER. CH^TOPODA. 



The Chsetopoda possess bristle-like appendages termed 

 setae. There are two sub-orders (1) Oligochseta, (2) Poly- 

 chaeta. The Oligochseta is unknown in the fossil state, 

 it includes the common earth-worm Lumbricus, 



SUB-ORDER. POLYCILETA. 



The members of this sub-order are nearly all marine, 

 they are characterised by the possession of numerous setae 

 which are placed on special processes termed parapodia. 

 Tentacles are present on the head. Many forms live in 

 tubes, which may consist of carbonate of lime, of chitinous 

 material, or of grains of sand cemented together by a 

 secretion. On account of the possession of this tube the 

 polychaetous annelids are often found fossil. Other forms, 



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