NO. 9 OLFACTORY SENSE OF INSECTS McTNDOO 2.J 



are nothing less than hairs inside of pits, and the only difference 

 between them is the shape of the flask. If they are olfactory organs, 

 odors must enter the small apertures and pass through the thin chitin 

 at the tip of the hairs inside the pits, to stimulate the sense fibers. 



In drones, the antennal organs are found on only the distal nine 

 joints of the flagellum and in workers and in queens on the distal 

 eight joints. x\ccording to Schenk, the pore plates are present on all 

 of these joints, and while they are abundant on both the dorsal and 

 ventral sides of the male antennae, in the female antennae nearly all 

 of them occur on the dorsal side. On both antennae of a male there are 

 about 31,000 and on those of a female only about 4,000; however, 

 those of the female are considerably larger. Pegs are entirely absent 

 from the drone antennae, while they are abundant on those of workers 

 and of queens. As a rule they are at the distal end of the joint on the 

 dorsal side. The male antennae are always devoid of tactile hairs 

 whereas those of the female have many. Forel's flasks and pit pegs 

 are moderately numerous in both sexes, but slightly less abundant in 

 the female antennae. 



Some of these antennal organs, or at least modifications of them 

 are present in the antennae of all species of insects with probably one 

 or two exceptions. In butterflies and moths pore plates are entirely 

 absent and pegs are almost wanting. However, the place of the pegs 

 seems to be taken by end rods, which are very similar in structure 

 but are more club-shaped. Butterflies and moths also have bristle- 

 like tactile hairs. 



Pore plates, pegs, Forel's flasks, pit pegs and end rods have all 

 been considered as olfactory organs by various authors, who, in trying 

 to prove their views, assert that odors can pass through the hard chitin 

 of these organs so that the nerve fibers inside may be stimulated. 

 While these authors declare that this is possible in insects, they ac- 

 knowledge that it would be impossible in the higher animals. 



Erichson (1847), according to Hicks (1859c), first observed the 

 pore plates and hairs on the antennae of insects. He considered the 

 pore plates as olfactory organs for two reasons: (i) He thought 

 that the numerous hairs on the antennae protect and keep these plates 

 moist, so that odors can pass through them, and (2) they are more 

 numerous in those insects whose smell is acute. 



Burmeister (1848) describes the pits found on the antennae of 

 lamellicorn beetles. These are a variety of the pit pegs, and he at- 

 tributes an olfactory function to them. 



Vogt (1851), according to Wonfor (1874), discovered that the 

 antennae are covered with minute pores which are apparently filled 



