EXTERNAL SKELETON OP INSECTS. 



85 



substance named Chitine, forms the base of it ; but there is reason 

 to believe, that it possesses a definite organic structure ; and 

 that it consists of one or more layers of cells, in the cavities of 

 which this substance is deposited. We see in it a great number 

 of pieces, which are sometimes soldered (as it were) together ; 

 whilst in other instances they are united by soft portions of the 

 skin, and thus possess a greater or less freedom of motion. 



661. The body of the Insect, as we have already said, is 

 divided into a certain number of rings, placed end to end ; and 



Head 



1st pair of Legs 



1st pair of Wings 

 2nd pair of Legs 



Thorax 



2nd pair of Wings 



3rd pair of Legs ~7 / '/ / VYM Abdomen 



Tibia 



Tarsus 



FIG. 393. ANATOMY OP THE EXTKRNAL SKELETON or AN INSECT. 



in this series of segments, we distinguish three portions, to which 

 are given the names of Head, Thorax, and Aldomen. The 

 members or appendages which spring from the several segments, 

 have a structure analogous to that of the trunk of the animal : 

 being composed of tubes or of hollow plates, placed end to end, 

 and enclosing in their interior the muscles and nerves destined to 

 put them in motion. 



VOL. II. H 



