STRUCTURE OF INSECTS. '285 



tropical insects display a gorgeous metallic lustre, 

 depending on the reflexion of the prismatic colours; 

 and the same variegated hues adorn the scales of 

 the butterflies of those reg-Jons. 



Hair grows in various parts of the surface of 

 insects.* Where the integument is membranous 

 and transparent, these hairs may be distinctly per- 

 ceived to originate from enlarged roots, or bulbs, 

 and to pass out through apertures in the skin ; as 

 is the case with the hair of the larger animals. 

 Their chemical composition, however, is very dif- 

 ferent, for they are formed of the same substance 

 as the integuments, namely entomoline. The pur- 

 poses served by the hairs are not always obvious. 

 In many cases they seem intended to protect the 

 integuments from the water, which they repel from 

 their surfaces. They tend to prevent injury arising 

 from friction ; and are accordingly found to be 

 more abundant in those parts, as the joints, which 

 are liable to rub much against one another: by 

 their elasticity, also, they help to break the force 

 of falls from heights. 



The divisions of the body are frequently marked 

 by deep incisions ; whence has originated the term 

 insect, expressive of this separation into sections. 

 It is, however, a character which they possess in 

 common with all articulated animals, the typical 

 form of which consists, as we have seen, of a series 

 of rings, or segments, joined endwise in the direc- 



* It is a singular fact, that almost all the insects which are found 

 in the South of Africa are furnished with a large quantity of hair. 

 This is particularly the case with the Buprestidce and Melalon- 

 t hides. 



