Xll PREFACE. 



mend recurring to one that has been in many 

 instances departed from. 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- 



