12 



THE INSECT WOELD. 



and the intestine, and urine alone when they are placed near the 

 posterior extremity of the alimentary canal. 



Fig. 11 represents part of the preceding figure more highly 

 magnified, showing the manner in which these tubes enter the 

 chylific ventricle. 



In our rapid description of the digestive apparatus of insects, it 

 only remains for us to mention certain purifying organs which 



secrete those fluids, generally 

 blackish, caustic, or of peculiar 

 smell, which some insects emit 

 when they are irritated, and which 

 cause a smarting when they get 

 into one's eyes. 



Less widely diffused than the 

 salivary organs, they are often of 

 a very complicated structure. In 

 Fig. 12 is represented the secre- 

 tory apparatus of the Carabus 

 auratus, which will serve for an 

 example : A represents the secre- 

 tory sacs aggregated together like 

 a bunch of grapes, B the canal, c 

 the pouch which receives the secre- 

 tion, D the excretory duct. 



Sometimes the secretion is 

 liquid, and has a foatid or ammo- 

 niacal odour ; sometimes, as in the Bombadier beetle (Brackinus 

 crepitans), it is gaseous, and is emitted with an explosion in the 

 form of a whitish vapour, having a strong pungent odour ana- 

 logous to that of azotic or nitric acid, and the same properties. 

 It reddens litmus paper, and burns and reddens the skin, which 

 after a time becomes brown, and continues so for a considerable 

 time. 



About the middle of the seventeenth century Malpighi at 

 Bologna, and Swamerdam at Utrecht, each discovered in different 

 insects a pulsatory organ occupying the median line of the back, 

 which appeared to them to be a heart. Nevertheless, Cuvier, 

 having declared some time afterwards that there was no circula- 



Fig. 12. Secretory apparatus of Carabus 

 auratus. 



