OF INSECTS. 
167 
and a little coloured oil. It may be placed in boil- 
ing water without undergoing any change ; the most 
highly concentrated acids are required to dissolve it. 
Except in one instance, (the female of the great 
aquatic beetle. Hydrous piccus,) this secretion is 
found only in lame, and in these the spinneret 
is usually situate in the mouth ; but in the larvae of 
Myrmelion it is in the opposite extremity of the 
body, like the spinning apparatus of spiders. This 
is likewise its position in the beetle just alluded to. 
To the secretion of poison , and the beautifully 
constructed instrument by which it is injected into 
the body of an enemy, insects are indebted for one 
of the most effectual means of defence which has 
been assigned to any kind of animal. It is limited 
to the Hymenoptera, and among these we are most 
familiar with its effects in bees and wasps. The 
poison is contained in a round or ovate bladder, lying 
very near the hinder extremity of the abdomen, and 
is discharged into the sting by a narrow duct, It is 
secreted by two very slender twisted vessels, which 
sometimes unite (as in the hive-bee. Apis mettifica >) 
into one tube at a little distance from their insertion 
into the bladder. The fluid is sharp and corrosive, 
and it is unnecessary to refer to the experiments of 
Reaumur to prove that it is the cause of the in- 
flammation and pain attending a puncture of the sting. 
The mere mechanical division of the tissues by so 
fine a point, would occasion comparatively little of 
either, as may be ascertained by making a puncture 
in the hand with a needle. The venom is a trans- 
