INTRODUCTION. 



II 



position. When they enter the chylific ventricle, they furnish only 

 bile; bile and a urinary liquid when they enter the posterior part 

 of the ventricle and the intestine ; and urine alone when they are 

 placed near the posterior extremity of the alimentary canal. 



Fig. ii 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 cer- 

 tain 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 well developed than the 

 salivary organs, they are often of a 

 very complicated structure. In 

 Fig. 1 2 is represented the secretory 

 apparatus of the Carabns anratus, 

 which will serve for an example : 

 A represents the secretory sacs 

 aggregated together like a bunch of 

 grapes, B the canal, c the pouch 

 which receives the secretion, D the 

 excretory duct. 



Sometimes the secretion is 

 liquid, and has a foetid or am- 

 moniacal odour; sometimes, as in 

 the Bombardier beetle (Brachinns 

 crepitans}, it is gaseous, and is 

 emitted, with an explosion, in the 

 form of a whitish vapour, having a 

 strong pungent odour analogous to that of 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 Swammerdam at Utrecht, discovered a pulsatory 

 organ occupying a median line of the back, which appeared t& 

 them to be a heart, in different insects. Nevertheless, Cuvier,. 

 having declared some time afterwards that there was no circula- 



Fig. 12. 



Secretory apparatus of Carabus auratus. 



