l89 6. LAMARCK AND LYELL. 93 



demand before we can believe that it has produced adaptive modifi- 

 cations is like the proof which would convince us that words and 

 sentences have fallen from a hopper filled with loose type. We must 

 have demonstrative evidence that no undiscovered adaptive mechanism 

 is at work. 



Those who hold, with Romanes, that we find in nature structural 

 adjustments which are inexplicable by selection alone, would do well 

 to rest on their oars and look about them for some other determinate 

 factor, or perhaps, for a better acquaintance with the resources, of 

 selection, before they attribute them, without demonstrative evidence, 

 to indeterminate "factors." 



W. K. Brooks. 



Johns Hopkins University, Baltimore, Md. 



