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 la Antennae 2 or 4. I.CRUSTACEA. 



2. Sac for respiration. Legs 12. Antennae none. 3 ARACHNOIDEA. 

 Q T i f f No antennae. 4. ACAIU. 



3. Trachea for \ r Six thoracic legs. 2. MYRIAPODA. 

 respiration. T antennB< -J Six thoracic legs, 7 ,- T,,^. 



but no abdominal.] 5 ' Ij> 



(248.) His divisions of the last class, or that of In- 

 secta, have been thus registered in the third volume of 

 his ec Zoological Miscellany : " 



I. Sub-class. ) 



AMETABOLIA. f Body ending in bristles. 



Nometamor- (" Body without bristles, 



phosis. ' 



II. Sub-class. 

 METABOLIA. 

 Metamorphosis - 

 triple. 



1. Thysanura. 



2. Anoplura. 



8. Coleoptera. 



4. Dermaptera. 



5. Orthoptera. 



6. Dictuoptera. Blatta L. 



7. Hemiptera. 



8. Homoptera. 



9. Aptera. 



10. Lepidoptera. 



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. 



