THE EVOLUTION OF MAN 



of the mouth has developed these into specially 

 strong and solid thorns, evidently for the good 

 purpose of holding on to the food of these fish. 

 This is a typical illustration of the genesis of 

 "teeth" and without this clue it would be a very 

 difficult problem to explain their origin. 



There are still further points of evidence. We 

 have just seen that the shark has the basic plan 

 of four limbs in the form of fins. The lamprey, 

 on the other hand, has none of that as yet, but it 

 has the beginning of a skull in a sort of skin and 

 cartilage* pouch. Amphioxus, finally, has not 

 even a trace of that. This would give us another 

 chain of evidence. XThe line of evolution seems* 

 to go upwards from Amphioxus by way of the 

 lamprey to the shark, and other things which we 

 observe at the same time fit very well into this x 

 ^outline. 



Throughout this region in the process of evo- 

 lution we find a number of details which do not 

 become intelligible until we meet them again in 

 very perfect forms in far higher stages. In the 

 life processes of some sharks, for instance, a 

 genuine placenta formation will suddenly appear, 

 the embryo being nourished through a placenta. 

 Like a flash of lightning the thought strikes us 

 that nature at this stage suddenly tried some- 



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