CHAPTER XII 

 THE WORM-LIKE ANIMALS 



293. The Worms. The word 



than a name for a shape, meaning an elongated animal with 

 cylindrical or ribbon-like body. The earlier naturalists 

 thought the shape very important, and so they placed all worm- 

 like animals together in a group which they named Vermes 

 (Latin for worms) ; but later studies have shown that worm- 

 like bodies may belong to animals which in all other points 

 of structure are seen to be totally unrelated. For this reason, 

 the group Vermes is not recognized in the recent textbooks 

 of zoology; but instead we find chapters devoted to such 

 groups as flat worms, round worms, segmented worms, and 

 others. There is such a vast assemblage of forms of the 

 worm-like animals that in a short course we can do no more 

 than select a few of the more interesting examples. 



294. The Flat Worms. These are the simplest worm- 

 like animals, and some of them are but slightly more complex 

 than some of the highest ccelenterates. Some of the common 

 species, known as planarians, are brown in color, from 

 J to \ inch long, and very easily found on the under side of 

 stones in fresh water streams and ponds. Small leeches 

 resemble them, but the leeches are easily distinguished by 

 the numerous rings around their bodies. The general appear- 

 ance of a common planarian is shown in Fig. 107. 



295. Other Flat Worms : Tape- Worms. All the ribbon- 

 like worms known as tape-worms are parasites in the ali- 

 mentary canal of vertebrate animals. They are simpler than 

 the flat worms, which live independently, for they have no 



340 



