20 PREFACE. 
pretension than that of heing actuated hy a sin- 
cere desire of rendering them accurate and faith- 
ful, in every particular, and, so far, worthy of 
acceptance. 
In bringing together and reviewing the labors 
of others in the same department of science, he 
has endeavored to do strict justice to all, to ac- 
knowledge his obligation for information received 
from each, and to indicate the source from which 
it is derived. If there are any omissions, in this 
respect, they have arisen from inadvertence and 
not from design. It will be noticed that in sev- 
eral instances he differs in opinion from those 
who have preceded him, and that he considers 
several species, described by them, to be merely 
varieties of, or even identical with, animals before 
known. In thus exercising his own judgment 
in opposition to that of persons for whose opinions 
he entertains the highest respect, he trusts that 
he has done it in a manner which cannot give 
just ground of offence. He has no regard for 
his own views, except so far as they shall be 
found consistent with truth, and he expects 
that they will be controverted by others with the 
same freedom, whenever they are supposed to be 
erroneous. 
