ARTHROPODA. 255 



267. The Thousand-legged Worms (Myriapoda). 



These are the lowest and simplest of the four classes of 

 arthropods. This is shown by the lack of differentiation 

 among the segments which suggests the segmented worms 

 and the larval stages of the insects. One division (the 

 centipeds (Fig. 101) are carnivorous and live on worms 

 and insects. A few of this group living in tropical regions 



FIG. iot. Centipede (Scolopendra heros). Photo by Folsom. Four-fifths natural 

 size. 



Questions on the Figure. What differentiation of segments is 

 apparent? Are there any fusions of segments into body regions? 

 What is the law of the occurrence of appendages? What diversity 

 is there among them? In what respects does this animal seem 

 intermediate between the annelids and the higher arthropods? 



are poisonous. The common ones are entirely harmless 

 to men, and the hurtfulness of the poisonous ones is 

 much exaggerated. The animals of the second division 

 (millipeds) have two pairs of legs on each segment. They 

 are vegetable feeders, have elongated rounded bodies, and 

 tend to roll up in a coil when disturbed. 



268. A Contrast of the Four Types of Arthropods: A Library 

 Exercise. Select a good representative of each of the four types of 

 arthropods: myriapod, crustacean, arachnid, and insect. By 

 means of parallel columns write a comparison of them in respect to 

 the following facts: 



