II 



THE EARLIEST KNOWN VERTEBRATES 



" We are the ancients of the earth 

 And in the morning of the times." 



There is a universal, and perfectly natural, desire for 

 information, which in ourselves we term thirst for 

 knowledge and in others call curiosity, that makes man- 

 kind desire to know how everything began and causes 

 much speculation as to how it all will end. This may take 

 the form of a wish to know how a millionaire made his 

 first ten cents, or it may lead to the questions — What 

 is the oldest animal? or. What is the first known 

 member of the great group of backboned animals at 

 whose head man has placed himself? and. What did 

 this, our primeval and many-times-removed ancestor, 

 look like? The question is one that has ever been full 

 of interest for naturalists, and Nature has been inter- 

 rogated in various ways in the hope that she might be 

 persuaded to yield a satisfactory answer. The most 

 direct way has been that of tracing back the history of 

 animal life by means of fossil remains, but beyond a 

 certain point this method cannot go, since, for reasons 

 stated in various places in these pages, the soft bodies 

 of primitive animals are not preserved. To supple- 

 ment this work, the embryologist has studied the early 

 stages of animals, as their development throws a side- 

 light on their past history. And, finally, there is the 

 study of the varied forms of invertebrates, some of 

 which have proved to be like vertebrates in part of 

 their structure, while others have been revealed as 

 vertebrates in disguise. So far these various methods 

 have yielded various answers, or the replies, like those 

 of the Delphic Oracle, have been variously interpreted 



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