192 ON SYSTEMATIC ZOOLOGY. 
(246.) It has been said “ that the principal merit of 
this system is the division of insects, tacitly pointed out 
by Fabricius, into two groups or sub-classes, from the 
mode in which they take their food.” If by this it is 
meant that these two sub-classes are natural, then they 
will form two circular groups exclusive of the Aptera, 
which they do not, even according to the circular theory 
which has been founded upon them. 
(247.) Dr. Leach, whose labours are so well known to 
entomologists, appears, according to Samouelle, to arrange 
the annulose types under five leading classes ; thus : — 
1. Gills for respiration. Legs 16. Antenne 2 or 4. 1. CRUSTACEA. 
2. Sac for respiration. Legs 12. Antenne none. 5 ARACHNOIDEA. 
; . gp, ( No antenne. 4. ACARI. 
3. pales SO } / Six thoracic legs. 2. Myriapopa. 
respiration. ¢ Two antenne. + Six thoracic lege, 5 ineeoun ) 
but no abdominal. §?" ~** ; 
(248.) His divisions of the last class, or that of Jn- 
secta, have been thus registered in the third volume of 
his “* Zoological Miscellany :”” — 
I. Sub-class. 
AmeraBoLiaA. ( Body ending in bristles. 1. Thysanura. 
No metamor- ( Body without bristles. 2. Anoplura. 
phosis. 
{ 3. Coleoptera. 
4. Dermaptera. 
| 5. Orthoptera. 
~ 6. Dictuoptera. Blatta L. 
: 7. Hemiptera. 
II. Sub-class. 8. Homoptera. 
METABOLIA. | 9. Aptera. 
Metamorphosis 4 10. Lepidoptera, 
triple. 11. Trichoptera. 
12. Neuroptera. 
13. Hymenoptera. 
14. Rhipiptera., 
15. Diptera. 
16. Omaloptera. 
(249.) We may now be allowed to close this enumer- 
ation of artificial systems, which serve to mark the rise 
and progress of systematic arrangement, but which ex- 
ercise very little influence on the present state of the 
science, pursued, as it now is, upon principles of in- 
ductive philosophy. There is, however, another mode 
of arrangement, which comes under this chapter, which 
we shall now shortly explain, and then dismiss. 
