52 



The Living Things of the Earth unit i 



Fig. 71 The house centipede enlarged. How do 

 you know that this is not a niillipede? (u. s, 



DEPARTMENT OF AGRICULTURE) 



The hundred- and thousand-legged 

 arthropods. A glance at the chart on 

 page 41 will show you members of two 

 more classes of arthropods, the "hundred- 

 leggers" and the "thousand-leggers." 

 Their bodies are made up of a series 

 of rings; that is why many persons think 

 that they are worms. But they have 

 jointed legs attached to each ring, and 

 their bodies have a firm covering. The 

 hundred-leggers or centipedes, have a 

 pair of legs on each ring. The thousand- 

 leggers, or millipedes, have two pairs 

 of rather short legs to a ring. Both these 

 classes are small and rather unimportant. 



The crustaceans. Another great ar- 

 thropod class, the crustaceans, includes 

 many forms that inhabit the sea, but 

 some live on land and some in fresh 

 water. 



It is difficult to state by what charac- 

 teristics you can recognize crustaceans. 

 About all that can be said here is that 

 if an animal seems to be an arthropod 

 and does not exactly fit into the insect, 

 spider, or centipede groups, it is prob- 



FiG. 72 Rock barnacles. These are crustaceans. 

 Almost 3000 of them have been counted on one 

 square foot of rock, (morris) 



ably a crustacean. The class includes the 

 lobsters and crabs, the crayfish, water 

 fleas, barnacles, shrimps, and hundreds 

 of other kinds. Study some crustacean at 

 first hand as described in Exercise 5. 



Some queer crustaceans. Perhaps all 

 crustaceans deserv'e to be called queer. 

 The lobster is just an ordinary kind of 

 crustacean; but it has eyes that are on 

 the ends of stalks, huge and powerful 

 pincers or claws, and it glues its eggs to 

 its legs. In spite of the saying "as red as 

 a lobster," live lobsters are not red at 

 all; only cooked lobsters are red. 



The crab, too, has eyes on stalks. 

 Its body is wider than long, and it seems 

 to have no abdomen. The queerest thing 

 about the crab is its walk. It walks side- 

 ways, but it manages pretty well. And 

 in the water it is a good swimmer. Along 

 the coast you can often buy soft-shelled 

 crabs. These are common crabs that 

 have recently lost their shells. All the 

 crustaceans with hard coverings shed 

 their coverings as their bodies become 

 too large for the shells. 



