BRANCH VERMES: THE WORMS 1 35 



stance either living or dead, some feed on living or 

 decaying plant matter. 



Classification. There is great lack of agreement 

 among zoologists in the matter of the classification of the 

 worms. Not only are the various groups which by some 

 are called classes held by others to be distinct branches, 

 co-ordinate in rank with the Echinodermata, Ccelenterata, 

 etc., but the limits of these groups are also constantly 

 called in question. It will require a great deal better 

 knowledge of the structure and life-history of these diverse 

 animals before the matter of their classification is satisfac- 

 torily settled. We shall consider briefly four of the 

 various groups (which we may consider as classes) which 

 include worms either specially familiar to us or of special 

 interest or importance. One or two examples of each 

 group (the groups being selected primarily because of the 

 examples) will be described in some detail. By this 

 means we may get an idea of the extremely diverse char- 

 acter of the animals which are included in the heteroge- 

 neous branch Vermes. 



Earthworms and leeches (Oligochaetae) . The various 

 species of earthworms, an example of which has been 

 studied are found in all parts of the world; they occur in 

 Siberia and south to the Kerguelen Islands. They are 

 absent from desert or arid regions, and some can live 

 indifferently either in soil or in water. Some near allies 

 ot the earthworms are aquatic, living in fresh or brackish 

 water, some in salt water near the shore. In size earth- 

 worms vary from I mm. (fa in.) to 2 metres (2^ yds.) in 

 length. All show the distinct segmentation of the body 

 noticeable in the common earthworm already studied. 



The leeches, some of which are familiar animals, are 

 closely related to the earthworms, although at first glance 

 the similarity in structure is not very noticeable. 



