EXTERNAL ANATOMY OF INSECTS. 353 



raniiSj Sprengel, Audoin, Chabrier, and, above all, M. 

 Cuvier in his celebrated Lectures on Comparative Ana* 

 tomy, have considerably extended the boundaries of our 

 knowledge in this department : and much of what I have 

 to say to you in my letters on this subject, will be derived 

 from these respectable sources. In the exterior anatomy 

 of insects, I flatter myself that I shall be enabled to make 

 some material additions to the discoveries of my prede- 

 cessors ; though few have occurred to me with respect to 

 their internal organization. 



In treating of the anatomy of the vertebrate animals^ 

 it is usual, I believe, to consider, first, the skeleton and 

 its integuments, whether of skin or muscle, and their 

 accessories ; and afterwards the organs of the different 

 vital functions and of the senses. But in considering 

 the anatomy of Insects, the difference before stated a , ob- 

 servable between them and the sub-kingdom just men- 

 tioned, as to their structure, renders it advisable to divide 

 this subject into two parts — the first treating of their 

 external anatomy, and the second of their internal. — 

 I shall begin by drawing up for you a Table of the No- 

 menclature of the parts of their external crust ; its ap- 

 pendages and processes b , external or internal, accompa- 

 nied by definitions of them ; and followed by such obser- 

 vations respecting them as the subject may seem to re- 

 quire for its more full elucidation. 



Anatomists have divided the human skeleton into three 



a See above, p. 43 — . 



b There are certain processes which are a continuation of the in- 

 ternal surface of the crust ; and serve, as well as the rest of it, for 

 points of attachment to the muscles : these, though completely in- 

 ternal, must be considered as parts of the external skeleton. 



VOL. III. 2 A 



