NO. 9 OLFACTORY SENSE OF INSECTS— McINDOO 5 



animals, unless it is to be assigned to the .a])ertures of tlie respiratory 

 organs. 



Of the foregoing six authors who advocate the theory that the 

 spiracles are the seat of olfaction, Lehmann is the only one who ex- 

 perimented on the subject. The others seem to think that an analogy 

 with higher animals is sufficient proof. Lehmann's experiments indi- 

 cate that the seat of smell is not located in the head and assumes that 

 the tracheae are the only other place in which these organs could be 

 located. No one has found any neryes or any kind of sense organ, 

 which suggest an olfactory function, in the walls of the tracheae or 

 in the spiracles of the bee. This theory has been long since 

 abandoned. 



STRUCTURE NEAR SPIRACLES AS SEAT OF OLFACTORY 



ORGANS 



Joseph (1877) postulated three conditions necessary for an olfac- 

 tory apparatus: (t) It must come in contact with moving air; (2) 

 it must' be continually moistened, and (3) the olfactory substance 

 must be in the form of a gas. If one of these three conditions is 

 lacking, olfaction is impossible. According to these conditions no one 

 has sought the seat of smell in any place other than at the entrance 

 of the tracheae, and the assumption that insects smell with their 

 antennae or buccal organs is completely inadmissible. In spite of the 

 fact that their antennae had been removed and in spite of their clumsy 

 flying, a number of Necrophorus vespillo (carrion beetles) found a 

 carcass wrapped in paper at a distance of 20 feet. The same result 

 was obtained with the flesh-fly (Musca) Sarcophaga carnaria and 

 with other insects. A -short distance from the spiracles, toward the 

 median line of the thorax and abdomen, he reports finding a peculiar 

 structure which he called the " regio olfactoria." This olfactory re- 

 gion is completely covered by a delicate membrane perforated by 

 pores, the largest of which are for gland exits and the smallest for 

 hairs. Beneath this membrane lies a peculiar layer of cells. 



Thus, not favoring the view that the spiracles are the seat of smell, 

 and in order to comply with the above three conditions, Joseph as- 

 sumed the existence of an organ near the spiracles which communi- 

 cates with the air cavities of the tracheae. Of course, being connected 

 with the tracheae and being continually moistened by the glands, it 

 is easy to see that the necessary conditions would be fulfilled. Xo 

 drawing of this organ is given and no such structure is found in the 

 honey bee. 



