12 THE INSECT WORLD. 
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. 
Hig. 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 feetid or ammo- 
niacal odour; sometimes, as in the Bombadier beetle (Grachinus 
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 Swammerdam at Utrecht, each discovered in different 
insects a pulsatory organ occupying a 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. 
