366 NATURAL ARRANGEMENT OF INSECTS. 



groups in equivalent circles correspond in some one 

 or more characters, peculiar to them alone, they must 

 be inevitably of the same value. 



(326.) Having now endeavoured to place the primary 

 divisions of apterous insects upon a more determinate 

 footing than has hitherto been done, we shall not attempt 

 to indicate, even by synthesis, the natural division of fa- 

 milies which must belong to each. Our object is to indi- 

 cate the road to natural arrangement, not to follow it up 

 in detail. The groups of the Aptera we have adopted, 

 are those of our predecessors : the only novelty consists 

 in an attempt to determine their relative value, and to 

 establish their relations to other groups. This done, we 

 shall, in the following pages, merely give the general 

 reader an idea of the insects contained in each, without 

 any attempt at determining their limits, or the system- 

 atic order in which the families should stand. 



CHAP. II. 



APTERA, continued. 



ON THE DIPTERA, ARACHNIDA, CRUSTACEA, MYRIAPODA, AND 

 SUCTORIA. 



(327.) NOT having thoroughly analysed the families 

 of which our circle of APTERA consist, we prefer giving 

 a rapid sketch of its contents, as investigated by the 

 latest and best systematists, to leaving the scheme im- 

 perfect by the omission. The first family comprised 

 within this circle are the Diptera ; and, although it 

 may appear a contradiction to speak of so large an order 

 of insects as the Diptera, under the general denomina- 

 tion of Aptera, yet, as they form the most aberrant sub- 

 family in the circle, this difficulty is removed, as they 

 constitute the direct point of contact with the pre- 

 ceding circle of the Ptilota. The Diptera comprise a 



