VI PREFACE. 



of lectures delivered at the Lowell Institute in 

 Boston, without any thought of their subsequent 

 publication. Notes were, however, taken of 

 them at the time, and I very willingly assented 

 to the suggestion of some of my listeners, that 

 they should be recorded in the form of articles 

 for the Atlantic Monthly. They still retain some- 

 thing of the repetition which is needed in a 

 public course of scientific lectures in order to 

 keep the connection of the subjects clearly before 

 the mind of a popular audience. An attempt 

 to change this character would have amounted 

 to writing the whole course anew, — a task for 

 which I had neither time nor inclination. I have 

 endeavored to avoid technicalities as far as pos- 

 sible in dealing with subjects many of which 

 are quite unfamiliar to the general mind ; and the 

 closing chapter of the book, which has been in- 

 corporated in the volume, but did not appear in 

 the Atlantic Monthly, is the only one especially 

 addressed to the professional naturalist. 



L. AGASSIZ. 



Nahant, August 22, 1863. 



