NO. 9 OLFACTORY SENSE OF INSECTS McINDOO 29 



beetles do not function as smelling organs. Also he infers, like 

 Leydig, that there may be some olfactory rods or pegs on the palpi 

 of this beetle. 



Gegenbaur (1870) briefly discusses the antennal organs described 

 by Erichson, Burmeister and Leydig but fails to express his own 

 opinion concerning their function. 



Lowne (1870) believes that the olfactory apparatus of the blow- 

 fly is located in the third antennal joint. This joint is remarkably 

 dilated and is covered with minute openings which communicate with 

 little sacs in the interior. 



Miiller (1871) found stiff hairs and pore plates on the flagella of 

 the antennx of a female bee, but only pore plates on those of the 

 male bee. He thinks that the pore plates are olfactory organs and 

 that male bees have a better olfactory sense than the females for the 

 following reasons : ( i ) A male bee has one more joint in the flagel- 

 lum; (2) all of these joints are longer, and (3) wider, and (4) the 

 pore plates are so close together that they crowd out the stiff hairs. 



Claus (1872) thinks that many insects have a well developed olfac- 

 tory sense and that the surface of the antennse is the seat of the sense 

 of smell, basing this conclusion upon the work of Erichson and that 

 of Leydig. 



Chadima (1873), after examining the hairlike structures on the 

 antennae and palpi of crustaceans, insects and myriapods, which 

 Leydig ( i860) regarded as most probably olfactory organs, says that 

 the smelling organs of arthropods have not yet been found. He states 

 that none of these hairs is perforated at its tip. He thinks investiga- 

 tors will have more success in solving this problem if they look on 

 the olfactory sense as being connected with the breathing apparatus. 



Forel (1874) counted five different kinds of organs on the antennae 

 of ants — (i) olfactory knobs or pegs, (2) tactile hairs, (3) pore 

 plates, (4) Forel's flasks and (5) pit pegs. Forel (1902) judging 

 from the works of Hicks, Leydig, Hauser, Krapelin and himself re- 

 marks that all the reputed olfactory structures of the antennae are 

 modified pore canals bearing hairs. They come under three chief 

 forms — pore plates, olfactory knobs, and olfactory hairs. At times 

 the last two can hardly be distinguished from one another. Chitin, 

 even if very thin, always covers the end of the nerve. Forel's flasks 

 and pit pegs have no relation to smell because they are lacking in the 

 insects with acute smell (wasps) and are present in great abundance 

 in insects (bees) with poor sense of smell. The same author (1908, 

 pp. 95 and 96) still regards the pit pegs and Forel's flasks as a 



