The Coming of Vertebrates and Rise of Fishes 



humble way, but because there are living 

 several curious little creatures whose true rela- 

 tions were for a long time unsuspected, though 

 they are now known to be vertebrates in dis- 

 guise. For Avhile the great current of life flows 

 ever onward, passing from lowly forms to those 

 of more complex pattern, yet this current has 

 its eddies w^here part of the stream may pause, 

 or even for a space flow backward. So while 

 animals as a whole move forward, some of them 

 drop out of the stream here and there and stand 

 still or even go backward or degenerate. This 

 may be brought about by adaptation to some 

 particular and easier mode of life, as when 

 creatures become mere parasites upon others ; 

 or it may be due to quite the reverse — to con- 

 ditions of life so severe that no progress is pos- 

 sible and a mere sim^^le existence is all that can 

 be achieved. We see this in mankind, both in 

 individuals and races. Man in general is better 

 housed, better clad, and better fed than he was 

 500 years ago, but some men to-day are not so 

 well oflf in these respects as were their ancestors 

 five centuries past. Just so with the race. In 



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