THE NEW EVOLUTION 



plants, such as the diatoms and peridinians (fig. 86, 

 p. i6i), as do some arthropods and the young of very 

 many fishes. A few, like the octopus, crawl about 

 the bottom and feed more or less after the fashion of 

 the crabs and lobsters. Still others, like the cuttle- 

 fish and squid (fig. 45, p. 97), live swimming freely 

 in the sea and successfully compete with fish. 



It is somewhat curious that while on the land the 

 creatures capable of the most rapid locomotion, the 

 running and flying animals, which are the dominant 

 types, are all vertebrates or arthropods, in the sea the 

 creatures with the greatest powers of locomotion, the 

 dominant swimming types, and all the flying types, 

 belong to the vertebrates and mollusks. In view of 

 the correspondence which exists on land between the 

 vertebrates and the insects in the matter of rapid loco- 

 motion we might expect that in the sea there would 

 be a similar correspondence between the vertebrates 

 and crustaceans. But instead we find that in the sea 

 the mollusks take the place of arthropods as effec- 

 tive swimmers. 



Perhaps the next most important of the major 

 groups, and a very large one, is that which includes 

 the jointed worms or annelids (fig. 85, p. 161). These 

 live mostly in the sea, but some live in fresh water 

 and a few upon the land — the earthworms, land- 

 leeches and onychophores (Peripatus). 



The jointed worms have the advantage over the 

 vertebrates and the arthropods in lacking a rigid 

 skeleton, either internal or external, which gives them 

 great flexibility. They have the advantage over 



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