HEXAPODA . 
77 
In arranging the orders in a linear series, as must be done in a 
book, it is impossible to indicate in a satisfactory way either the rela¬ 
tion of the orders to each other or the relative rank of the orders. 
An effort is made to place near together closely allied orders, and to 
treat first those that are more simple or primitive or generalized in 
structure, and last those that are more specialized. But this plan 
could be fully carried out only by having several parallel columns on 
the pages of the book, each representing a distinct line of descent, 
an arrangement which, to say the least, is impracticable. 
What has been done in this work is to place first the Thysanura, 
which is doubtless the most primitive order. Then follow first the 
orders that undergo an incomplete metamorphosis, and last, those 
that undergo a complete metamorphosis. Within these two groups of 
orders those with biting mouth-parts are placed first, and these are 
followed by those with sucking mouth-parts, except that in the 
second group the Coleoptera and Hymenoptera are placed last for 
want of a better position. We do not intend to indicate by this that 
these two orders are closely related, or that they are more specialized 
than the Diptera. 
In fact, with regard to at least five of the orders of insects (Hemip- 
tera, Lepidoptera, Diptera, Coleoptera, and Hymenoptera), it seems 
idle to us to discuss which is the more highly specialized. Each has 
been specialized in a direction peculiar to itself ; and to attempt to 
describe which is the “highest" seems as futile as the discussion by 
children of the question : “ Which is better,sugar or salt? ” 
We give below a table for use in classifying specimens. This table 
is merely intended to aid the student in determining to which of the 
orders a specimen that he is examining belongs. No effort has been 
made to indicate in the table the relation of the orders to each other. 
TABLE FOR DETERMINING THE ORDERS OF HEXAPODA.* 
( This table includes only adult insects.) 
A. Wingless or with rudimentary wings. 
B. Mandibles and maxillae retracted within the cavity of the head 
so that only their apices are visible, p. 82. Thysanura. 
BB. Mandibles and maxillae more or less prominent and fitted for 
biting. (See BBB also.) 
C. Head with long, trunk-like beak. ( Boreus .) p. 184. 
Mecoptera. 
* See note at bottom of p. 10. 
