NO. 9 OLFACTORY SENSE OF INSECTS McIXDOO 4I 



internal structure of these organs, and the latter is drawn diagram- 

 matically. In this he fails to show the chitinous cone, and the end 

 of the sense fiber is represented as separated from the exterior by 

 the thiiT layer, forming the dome. On this incorrect interpretation 

 of the anatomy, he, like Guenther, speculates on their probable func- 

 tion and concludes that these sense domes may serve as some kind 

 of a barometric device or as an apparatus for measuring the force 

 of the air against the wing. 



Berlese (1909, pp. 678-684) calls all the dome-shaped organs of 

 insects " sensilli campaniformi o papilliformi." The campaniform 

 type is found on the mandibles, antennae, legs and wings. Their 

 domes never project above the general surface of the surrounding 

 chitin. The papilliform type occurs only on the halteres. Here the 

 domes project above the surface of the chitin. In schematic draw- 

 ings he shows how the domes may have been derived from a portion 

 of the chitin originally not arched. Berlese regards the function of 

 these organs as unknown. 



While studying the morphology of the chordotonal organs in the 

 honey bee and ants, Schon (1911) found two rows of small cones on 

 the proximal end of each tibia. A sense cell lies just beneath each 

 cone and the peripheral end of the sense fiber runs into the cone. 

 These sense cells connect with the chordotonal organ located in the 

 middle and distal end of the tibia. Schon has certainly mistaken 

 Hicks' vesicles for cones, because the external appearance of these 

 vesicles often resembles ''ones when observed without the cylindrical 

 tibia being properly rotated. These organs always lie near the edge 

 . of the tibia, and when one looks down upon them their apertures look 

 like cones, but when the tibia is rotated slightly, so that they lie on the 

 median line of the tibia, the optical illusion becomes evident. 



Hochreuther ( 1912) describes and gives drawings of the dome- 

 shaped organs (kuppelformigen Organe ) in a manner somewhat 

 similar to that of Janet. Each organ is located at the bottom of a 

 chitinous flask, the mouth of which communicates with the exterior. 

 Instead of the peripheral end of the sense fiber coming into direct 

 contact with the air in the flask, it apparently stops just beneath the 

 chitinous dome. No true chitinous cone is present, but his terminal 

 strand (Terminalstrang) resembles it somewhat in general appear- 

 ance. He finds a few of these dome-shaped organs on the epicranium 

 near the margin of the eyes, 11 on the first and second joints of the 

 antennae, a few on the dorsal side of the labrum, very few on the 

 dorsal side of the mandibles, several on the maxillae, about 18 on the 

 first four joints of the first legs, about 10 on the first three joints of 



