INSECTS — SEAT OF THE SENSE OF SMELL. ^5 



organs described by Hancock in Gasteropoda, and by 

 Leuekart in Pteropods, as olfactory, seems very doubtful. 



As regards the seat of the sense of smell in insects, 

 there have been four principal theories. It has been 

 supposed to reside — (1) In the spiracles, or breathing 

 holes ; (2) in tlie neighbourhood of the mouth ; (3) in 

 the antennae ; (4) in different parts of the body. The 

 history of the question has been well given byKraepelin 

 in an admirable memoir, " Ueber die Geruchsorgane 

 der Gliederthiere." * 



Sulzer, in 1761,t suggested that the organ of smell 

 was probably to be found in the neighbourhood of the 

 spiracles, or breathing-holes. It is hardly necessary to 

 observe that insects do not breath as we do, through 

 their mouths, but through a series of orifices along the 

 sides, leading into trachesB, or air-tubes, which ramify 

 throughout the body ; so that the blood is aerated, not 

 in one special organ, but throughout its course. Now, 

 it is important that a more or less continuous current 

 of air should pass over the surface of the organ of 

 smell, as it is in this manner brought in contact with 

 the odoriferous particles. In man and the other air- 

 breathing vertebrates, the combination of the entrance 

 to the lungs with the nose and mouth offers great 

 advantages. The olfactory organ is brought close to 

 the mouth, where it is especially useful in the exami- 

 nation of food ; while the continuous current of air 

 necessary to respiration is utilized in the production 

 of sound, on the one hand, and in bringing odoriferous 

 particles to the organ of smell, on the other. 



* Separat Abdruok aus dem Osterprogramm der EealsoUule des 

 Johanneum." 1883. 



t " Gesohichte der Insekten." 



