SUB-KINGDOM V. VERMES. 



Classes. Orders. 



1. Platyhelminthes. 



2. Nemathelminthes. 



3. Rotifera. 



(1. Chaetopoda.... \ 

 I 2. Oligochseta. 

 2. Gephyrea. 

 3. Hirudinea. 



THE worms include a large number of animals which 

 differ considerably in their plan of organisation and thus 

 form a very artificial group. The body is bilaterally 

 symmetrical and has generally an elongated form. In some 

 it is unsegmented, in others it is divided into somites. 

 Lateral appendages are often present, but they differ from 

 those of the Arthropods in being unsegmented. A nervous 

 system and generally a blood vascular system and ali- 

 mentary canal are present. A large number possess no 

 skeleton and consequently the palseontological history of 

 the sub-kingdom is extremely imperfect. 



The worms may be divided into four classes, (1) Platy- 

 helminthes, (2) Nemathelminthes, (3) Rotifera, (4) An- 

 nelida. The Platyhelminthes and Rotifera are unknown 

 in the fossil state, the former includes the liver-fluke, 

 tape- worms etc. (e.g. Distomum, Tcenia, Planaria), the 



