INSECTS IN GENERAL. 57 



" because, from analogy its existence has been always sought 

 for somewhere about the head." It is but justice, however, 

 to remark that Mr. Spence (we believe) has advanced strong 

 probabilities in favour of the antennce being the auditory 

 organ, notwithstanding what we have already cited in treat- 

 ing of those appendages. 



" As to the organ of smell, when we reflect on the nature 

 of this perception," says M. Dumeril, " we are surprised 

 that physiologists have desired, by no very judicious ana- 

 logy, to find towards the head of insects the instrument in- 

 tended to arrest odours, and appreciate their qualities. Mam- 

 mifera, birds, and reptiles, are organized like man in relation 

 to the olfactory sense, as they all respire by lungs, and the 

 air which penetrates into their body for this purpose, can 

 travel but by one road, which is the double entrance of the 

 nostrils. It is on this forced passage, and on the very orifice, 

 that the trial of the nature of this air must be made, to ad- 

 vertise the animal of the danger of admitting it, or the neces- 

 sity of expelling it. 



" Odours, in fact, have the greatest analogy with tastes. 

 They consist materially of the particles of bodies held in 

 suspension, some in gases, some in other fluids. The elastic 

 fluids continually dissolve bodies at their surface, by which 

 means, they are charged with some atoms of their constituent 

 parts, and they retain them thus suspended in a sort of solu- 

 tion, disposed however, to abandon them when they shall 

 have a greater tendency to unite with other substances. 

 Under some circumstances, very volatile substances, and 

 often in consequence very odorous, assume momentarily the 

 form of vapours, or impermanent gases, which possess most 

 of the properties of the air, or of the elastic fluids with 

 which they mingle. It is in this point of view, and as gasei- 

 fied corpuscles, or aeriform fluids, that the operation of 

 odours ouirht to be studied." 



