234 GENERAL ZOOLOGY 



shown by the arrows. Through two of these improvised tubes 

 solid (microscopic) food is carried in ; through the middle one 

 the unused particles and the excreted wastes of the body are 

 sent away. The bristles are useful in affording a surface 

 for microscopic organisms to grow, which later become food 



for their larger table-mate ; the 

 bristles are also useful in pre- 

 venting sand from entering the 

 cavity between the valves. 



The internal organs are very 

 much the same as in Pluma- 

 tella. In fact, 

 the nearest liv- 

 ing relatives of 

 Lingula and its 



close allies, the 

 FIG. 117. Brachiopod. Enlarged. (After Morse) 



members of the 



class Brachiop'oda, are thought to be the class Polyzoa. 

 Brachiopods are among the oldest of animal groups. The 

 valves of ancient brachiopods found in strata of rock indi- 

 cate that the class, many millions of years ago, was far more 

 abundant than it is now, and also that the structure of the 

 animals has changed little in all that time. 



O 



The phylum represented by Plumatella and Lingula is 

 known by the name Molluscoi' da, because of their formerly 

 supposed relationship to the Mollusca. 



Definition of Vermes (Lat. vermis, a worm). The task of 

 summing up the characteristics of the Arthropoda was a 

 comparatively simple one, but the " worms" comprise such 

 a varied lot of widely different forms, that no important set 

 of structural characteristics can be found that tends to unite 

 them into a clearly defined group. The old systems of classi- 

 fication employed the term " Ver'mes " as the name of a sub- 

 kingdom, to include all those animals that had a long, slender, 



