72 MEANING OF ORDERS. 
CHAPTER V. 
DIFFERENT VIEWS RESPECTING ORDERS. 
It is in the search after the true boundaries 
and characteristics of orders that we may expect 
the greatest advance by the naturalists of the 
present day; and yet there is now much discre- 
pancy among them, some mistaking orders for 
classes, others raising families to the dignity of 
orders. This want of agreement in their results 
is not strange, however; for the recognition of 
orders is indeed exceedingly ‘difficult. If they 
are, as I have defined them, groups in Nature 
founded upon a greater or less complication of 
structure, they must, of course, form a regular 
gradation within the limits of their class, since 
comparative perfection implies comparative rank, 
and a correct estimate of these degrees of com- 
plication requires an intimate and extensive 
knowledge of structure throughout the class. 
There would seem to be an arbitrary element 
here, — that of our individual appreciation of 
structural character. If one man holds a certain 
kind of structural characters superior to another, 
