VI PEEFACE. 



The Authors gratefully acknowledge the aid they have re- 

 ceived in preparing the illustrations and working out the 

 details from Mr. E. Desor, for many years an associate of Pro- 

 fessor Agassiz ; from Count Pourtales and E.C.Cabot, Esq.; 

 and also from Professor Asa Gray, by valuable suggestions in 

 the revision of the letter-press. 



The present volume is devoted to Comparative Physiology 

 as the basis of classification ; the second will comprise Sys- 

 tematic Zoology, in which the principles of classification will 

 be applied, and the principal groups of animals briefly charac- 

 terised. 



Should our aim be attained, this work will produce more 

 enlarged ideas of man's relations to Nature, and more ex- 

 alted conceptions of the plan of Creation and its Great 

 Author. 



BOSTON, JUNE 1, 1848. 



