46 



TRANSFORMATIONS OF INSECTS. 



button-holes, which are usually situated upon the sides of the body. 

 When a smooth-skinned, light-coloured caterpillar is examined, 

 these orifices or spiracles can be seen ornamenting its sides. Their 



A TRACHEA MAGNIFIED. 



margins are rather hard, and are tinted black, red, orange, or 

 brown. Most frequently the spiracles are placed exactly on thej 

 sides of the body, and there is a pair for the prothorax and a 

 pair for each of the first eight segments of the abdomen. The 

 spiracles are not found on the mesothorax and metathorax, which 

 sustain the wings, but these organs are full of 

 tracheae. Nature has arranged the position of the 

 spiracles in some insects with an evident design ; 

 thus in the larvae of many flies there is only one 

 pair of spiracles, and these external organs of res- 

 piration — mouths, as it were — are situated quite at 

 the end of the body. Were it not so the larvae 

 would soon be stifled, for they dig deep into the 

 bodies of the unfortunate creatures they infest, 

 and feed luxuriantly, being embedded in their 

 nourishment. When a man eats voraciously he 

 often has to stop to take breath, and no one can 

 drink for any length of time without doing the same ; but these 

 parasitic larvae gormandise fearlessly. They breathe through the 

 spiracles in the end of their bodies which are left sticking out in 

 the open air. Many of the larvae that bury themselves in decom- 

 posing animal and vegetable matters breathe safely in this manner. 



A SPIRACLE 



