394 GREAT STEPS IN ORGANIC EVOLUTION 



for dealing with frequently ree-irrent injuries such as lost 

 arms in starfishes and broken legs in crabs, and so on through 

 a long list. 



We can only allude to the establishment of the leading 

 types of architecture which are represented by the various 

 series of Invertebrates or backboneless animals. Besides and 

 beyond the sponges and Coelenterates already spoken of, we 

 have to deal with a perplexing variety of worm-types; with 

 the higher segmented worms or Annelids, probably leading 

 on to Vertebrates; with the starfishes, sea-urchins, and the 

 like forming the series of Echinoderms; with the jointed- 

 footed Arthropods, such as crustaceans, insects, and spiders, 

 in which instinctive behaviour reaches its climax; with the 

 unsegmented limbless Molluscs, such as bivalves, snails, and 

 cuttles; and many a smaller group besides. 



To what purpose such enumeration ? Simply that we 

 must bear in mind the fact that millions of years are spent 

 in the fashioning of minutiae of perfection in types which 

 are certainly not near the highway of evolution that led to 

 backboned animals and eventually to man. Nothing is too 

 remote, too minute, too trivial — everything must be finished 

 and refined. Though it take a million years to make an 

 Argonaut, there is no hurry. 



§ 8. Rise and Progress of Backboned Animals. 



But a step of great magnitude among many that were 

 eventful was the oris^in of backboned animals or Vertebrates, 

 which perhaps emerged from an Annelid stock. The origin 

 of Vertebrates meant an independent start on a new line 

 of more masterful life. A dominant feature was the es- 

 tablishment of a relatively large brain protected by a skull 

 and of a long spinal cord protected by the backbone. For 



