THE METAZOA 



mist can often reconstruct an animal from 

 a single tooth. 



All these internal adjustments present 

 at last an infinitely more complex and 

 complete mechanism than the watch which 

 Paley instanced as an illustration of in- 

 telligent design in the making. Paley's 

 argument, however, in our times has heen 

 quite displaced by the great conception of 

 mechanical development, or as it is called, 

 Evolution, a conception which while true 

 enough in principle is so far wholly im- 

 provable in details. Evolution through 

 descent of the later from earlier forms is 

 believed in by all biologists, however di- 

 verse their opinions about what the process 

 of evolution itself was. But here comes 

 the great difficulty, namely, that general 

 descent does not afford the least insight 

 into individual descent. The real problem 

 of life, therefore, is how the microscopic 

 single cell, with which each individual 

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