PART II — WORMS 



CHAPTER XI 

 INTRODUCTION TO THE "WORMS" 



Classification. — The name worm is an indefinite tiiough sug- 

 gestive term wliich is popularly applied to any elongated creeping 

 thing which is not obviously something else. There is hardly 

 a branch or phylum of the Animal Kingdom which does not 

 contain members to which the term " worm " has been applied, 

 not excepting the great group Chordata, to which the back- 

 boned animals, including man himself, belong. In fact some 

 animals, such as many insects, are " worms " during one phase 

 of their life history, and something quite different during another. 



In a more restricted sense the name " worm " is applied to three 

 great groups of animals, with a few outlying forms, wliich super- 

 ficially all resemble one another in being unquestionably " worm- 

 like," though in life and structure they are widely different. 

 To these animals, together with a few other heterogeneous forms, 

 the collective name " Vermes," meaning worms, was applied by 

 the early workers on zoological classification. Upon more de- 

 tailed study it became obvious that different types of the " Ver- 

 mes " differed from one another to such an extent that they 

 would have to be divided into several great branches or phyla of 

 the Animal Kingdom. At the present time the majority of these 

 animals are classified in three phyla, as follows: the Platyhel- 

 minthes or flatworms, the Nemathelminthes or roundworms 

 and the Annelida or segmented worms. There are a number of 

 " worms " which will not readily fit into any of these groups but 

 are incertce sedis, showing affinity to one group in some respects 

 and to another in others. Some species are so profoundly modi- 

 fied by their peculiar modes of life that it is practically impossible 

 even to guess at their true relationships. AH three of the phyla 

 of " worms " contain parasitic species, though none of them con- 

 tain parasites exclusively. 



Flatworms. — The group of lowest organization is the Platyhel- 

 minthes. The worms included in this phylum are flattened 



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