34- Laboratory Guide in Zoology 



The lowest of th6se branches into which the old group 

 Vermes has been broken up, is the branch Platyhelmin- 

 thes, which includes the so-called Flatworms. These are 

 soft-bodied, bilaterally symmetrical animals in which the 

 body is generally compressed above and below so as to 

 give a flattened appearance. There is not a distinct body 

 cavity. This group includes many species, some of which 

 live free in water of ponds and streams, while others are 

 parasites; the tapeworm of man is an example of the 

 latter. 



The next higher branch is called the Nemathelminthes, 

 and includes the so-called Roundworms or Threadworms, 

 the " Hook-headed worms," and the " Arrow-worms." In 

 general the body is cylindrical. The most important class 

 is the Nematoda, which includes the "vinegar eels" and 

 various small worms that live as parasites in the roots of 

 plants, as well as the Trichina spiralis found in pork and 

 often causing disease in man. 



The third group which has been separated from the 

 Vermes is the Trochelminthes already discussed, while 

 the fourth is the MoUuscoida. This is composed of three 

 classes ; namely : — =- 



I. Polyzoa. The " Sea-Mats " and " Corallines." 

 II. Phoronida. Phoronis, a worm-like animal living in 



the sea. 

 III. Brachiopoda. The Lamp-shells. 



