274 



METAZOAN PHYLA 



sticky slime is ejected from the oral papillae. This indicates that this 

 is a weapon of defense, although it ordinarily serves in the capture of 

 small insects and other animals used as food (Fig. 176). Owing to the 

 velvety texture of the skin and its rich coloring, Onychophora are 



described by Sedgwick as animals "of striking 



beauty." 



308. Myriapoda. — Myriapoda (mir i ap' oda; 

 G., myrios, ten thousand, and podos, foot) is a 

 third class distinguished particularly by four 

 characteristics: (1) The metameres are many, 

 all metameres back of the head are alike in 

 appearance, and there are numerous pairs of 

 similar running legs; (2) the head has a pair of 

 antennae, a pair of mandibles, and one or two 

 pairs of maxillae; (3) the animal breathes by 

 tracheae opening to the outside by metamerically 

 arranged pores; and (4) the excretory organs are 

 malpighian tubules, like those present in insects, 

 opening into the posterior end of the intestine. 

 The body of all myriapods is elongated, some- 

 times nearly cylindrical and at other times 

 dorsoventrally flattened, rarely being com- 

 pressed from side to side. Myriapods are widely 

 distributed and flourish under a variety of condi- 

 tions. The class is divided into several orders, 

 two of which are larger and better known than 

 the rest, one including the centipedes and the 

 other the millipedes. 



309. Centipedes. — The centipedes, or hun- 

 dred-legged worms (Fig. 177), have a body 

 which is, generally speaking, flattened dorsoven- 

 trally and which may consist of from as few as 



15 to as many as 175 or even 200 metameres. Each of these metameres, 

 except the last two and the one just behind the head, bears a pair of 

 legs. The one next to the head has a pair of poison claws, or maxillipeds, 

 by means of which the animal kills the other small animals which it uses 

 for food. 



Centipedes are active, rapidly moving myriapods living under the 

 bark of logs and objects lying upon the ground. They are predaceous, 

 catching and devouring any living animals which they are able to over- 

 come. In tropical countries they reach a considerable size, sometimes 

 a foot in length, and the bite of such a centipede is often painful, although 

 not ordinarily dangerous to human life. A form known as the house 

 centipede, Scutigera, is common in the southern, western and central 



Fig. 177. — A Tropical 

 American centipede, Scolo- 

 pendra sp. From a dried 

 specimen. X %. 



