THE ORGANS OP THE SENSES. 301 



their object ? Where the palpi are the sheaths of the proboscis, as in 

 the Lepidoptera and Hemiptera, they could no longer remain true 

 organs of touch ; and where they have grown into a fleshy proboscideal 

 sheath, as in the flies, this sheath is the organ of touch, and properly, 

 also, the palpus itself is considered as contained in it. If, however, 

 living insects have been observed, no further objection will be taken to 

 the exclusive function of touch exercised by the palpi ; who still doubts 

 who has observed the play of the palpi of the spiders previous to copu- 

 lation, or seen predatory insects fall upon an unexpected prey, and 

 feeling it upon all sides ? The common, well-known, domestic fly, 

 lastly, can daily convince us, when we perceive it moving from spot to 

 spot, and detect every drop of liquid and every atom of sugar with 

 the sheath of its proboscis formed of the labial palpi. It first feels 

 them, and then ravenously swallows them ; but this touch is never 

 exercised by its tarsi, but invariably by the sheath of its proboscis. 



