374 STRUCTURE Otf INSECTS, 



face, and not of refraction from the inner parts of the 

 covering. It is the varying colour of the pigeon's neck, 

 or of shot silk, and not that of a mother-of-pearl shell 

 or an opal, it arises from minute surfaces of different 

 colours intermixed, and not from laminae or plates, of 

 different texture and transparency, placed the one over 

 the other. In short, it is probably the most plastic, 

 and therefore the most curious substance in nature, 

 being of all hues and all consistences, and adaptable 

 to all purposes ; and yet in its composition always the 

 same. It forms - the fine down or feathers upon the 

 moth and butterfly, the large nervous wings of the 

 dragon-fly, trie sting of the bee, the crust of the beetle ; 

 and it is very doubtful whether it does not also form 

 the web of the spider, and even the cocoon of the silk- 

 worm. 



But there is a further uniformity of purpose in the 

 muscular structure of insects in those organs that move 

 their little feet, their wings, their jaws, and their won- 

 derful antennae or feelers. Those muscles, downward 

 as far as the microscope can follow them, are of the 

 same fibrous texture as the muscles of large animals ; 

 but as they do not, like these, move over internal ful- 

 crum bones, they are without tendons, and have their 

 fibres inserted immediately into the covering or crust. 



The body of an insect was, by Linnaeus, regarded as 

 made up of three parts, the head, the trunk, and the 

 abdomen ; but as the middle part, or trunk, consists of 

 two distinct portions, more modern naturalists have 

 considered the whole body as made up of four, the 

 head, the thorax, the breast, and the abdomen. The 

 relative proportions of those parts, and also the mode 



