IX. 

 PALEONTOLOGY. 



I will now consider the theory of evolution with 

 regard to vertebrates. 



Having written of the " ideal primitive vertebrate" 

 as imagined by Haeckel, Professor Eomanes says: 



" Now I should not have presented this ideal repre- 

 sentative of a primitive vertebrate, for I have very 

 little faith in the ' scientific use of the imagination ' 

 where it aspires to discharge the functions of a creat- 

 or in the manufacture of archetypal forms — I say I 

 should not have presented this ideal representative of 

 a primitive vertebrate, were it not that the ideal is 

 actually realized in a still existing animal. For there 

 still survives what must be an immensely archaic 

 form of vertebrate, whose anatomy is almost identical 

 with that of the imaginary type which has just been 

 described. I allude, of course, to Amphioxus, which 

 is by far the most primitive or generalized type of 

 vertebrated animal hitherto discovered. Indeed we 

 may say that this remarkable creature is almost as 

 nearly allied to a worm as it is to a fish. For it has- 

 no specialized head, and therefore no skull, brain or 

 jaws; it is destitute alike of limbs, of a centralized 

 heart, of a developed liver, kidneys, a^nd in short of 

 most of the organs which belong to the other Verte- 

 brata. It presents, however, a rudimentary backbone, 

 in the form of what is called a notochord. Now a 

 primitive dorsal axis of this kind occurs at a very 

 early period of embryonic life in all vertebrated ani- 

 mals; but with the exception of A.mphioxus, in all 



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