Vlll PREFACE. 



In conclusion, I have to acknowledge my indebtedness 

 to Mr. Philip Lutley Sclater, of Corpus Christ! College, 

 Oxford, for his kindness in revising the proofs of this 

 edition, a tedious task, which could only be entrusted to 

 one extensively conversant with the literature of our 

 science, and which he has executed with great care. 



L. AGASSIZ. 



CAMBRIDGE, MASS., 



2nd December, 1858. 



