Xll PREFACE. 



mend recurring to one that has been in many 

 instances departed fi'om. We ought in every 

 division of the animal kingdom to look for one 

 great principle, or basis of arrangement, in a struc- 

 ture which exists throughout nearly the whole of 

 the animal creation ; and which structure, both as 

 regards its anatomical and physiological develope- 

 ment, becomes gradually of more and more impor- 

 tance, as we trace it upwards from the lowest beings 

 in which it exists to the highest. This structure, 

 I need scarcely remark, is the nervous system ; 

 but although it constituted the chief character, or 

 principle followed by Naturalists in the arrange- 

 ment of the vertebrated animals, it has very singu- 

 larly been much deviated from by them, and is 

 rendered of scarcely more than secondary considera- 

 tion in their arrangements of the Invertebrata. 



It is with reference, then, to the comparative 

 developement of the nervous system that I would 

 attempt to arrange insects, since I have no doubt, 

 that when we have become better acquainted with 

 the forms of their nervous system, the characters 

 will be found as marked in them as in the Verte- 

 brata. In following this mode of arrangement it 

 will be seen, that some of the vegetable feeders will 

 stand before the carnivorous. Thus the Lamelli- 



