viii A PREFATORY LETTER. 



If you find its phraseology, in some places, to be more 

 vigorous than seems needful, recollect that it was written 

 in the heat of our first battles over the Novum Organon 

 of Biology ; that we were all ten years younger in those 

 days ; and last, but not least, that it was not published 

 until it had been submitted to the revision of a friend 

 for whose judgment I had then, as I have now, the 

 greatest respect. 



Ever, my dear Tyndall, 



Yours very faithfully, 



T. H. HUXLEY. 



London, June 1870, 



