ARTHROPODA 77 



possessing what is termed metameric symmetry, 

 but they are distinguished from them as the 

 Leggy Animals, a fact which is explained in the 

 name, Arthropoda, joint-footed. Worms, as we 

 have seen, have no true legs, but 

 the Arthropods, theoretically, have 

 a pair of legs to every ring. In 

 some of the lower members of the 

 group this is literally the case, the 

 Centipedes, or hundred-footed ani- 

 mals, for example (Fig. 13). In 

 higher forms the number of legs 

 is greatly reduced ; several suc- 

 cessive rings may become merged 

 with one another, losing, along with IG ' 

 their independence, their legs. The 

 true Insects, thus, have only three 

 pairs of legs and the Spiders four. m size. 



What are theoretically regarded 

 as legs, however, may practically be turned to 

 many other uses, according to the position of the 

 particular body-ring to which they are attached. 

 Thus, in the case of a body-ring near the mouth, we 

 find such things as " jaw-feet," maxillipedes that 

 is to say, legs used for jaws. It consequently re- 

 sults that zoologists are sometimes driven to speak 

 of " walking legs," or, hiding the tautology under 

 a Latin phrase, " ambulatory legs " ; and absurd 

 although this may seem, it is sometimes quite 

 necessary for the sake of accuracy. It is therefore 

 more convenient to speak of the " appendages " 

 of a body-ring than of its legs. For this vague 

 term can be applied equally to all the row, what- 

 ever their uses. Among the different forms taken 

 by the " appendages " are those of " antennas," 

 long, hair-like feelers attached to the head; 



