THE OLFACTORY SENSE OF COLEOPTERA. 421 



cone (Fig. 9, Con) never occupies more than one fourth of the 

 pore cavity and usually much less (Fig. 12, Co7i). The cone 

 always stains less deeply than the surrounding chitin, and it is 

 common to see a hypodermal secretion (Figs. 9 and 10, HypS) 

 inside the pore cavity. The sense fiber (Fig. 9, SF) pierces the 

 cone, and the chitin between the pore aperture and the cone, and 

 it ends in the bottom of the pore aperture or pit (Figs. 9-12, P) 

 with its peripheral end exposed to the air in the pit. 



The second type of pores is found in the legs of Orthosoma 

 (Figs. 13-15), although the pores in the elytra (Fig. 21) and 

 wings (Fig. 31) of the same beetle belong to the first or most 

 common type. The chitinous integument of the legs of Ortho- 

 soma is thicker than that of the legs of any other beetle examined. 

 Instead of the sense cells (Fig. 13, SC) lying in the lumen of the 

 legs outside the pore cavities, in this type they lie inside the 

 pore cavities. When the chitin forming the wall of the pore is 

 not thick enough to protect the entire sense cell, the wall of the 

 pore projects flange-like (Fig. 14, Fl) into the lumen of the leg. 

 In Fig. 14 only about one third of the sense cell (SC) is shown. 

 Studies of the olfactory pores in various hymenopterous insects 

 made by the writer have shown that the sense cells begin to 

 differentiate at the time when the chitin is beginning to be 

 formed. From this fact, it is quite probable that the sense cells 

 found in the second type of pores have not migrated into the 

 pore cavities, but they now remain in approximately the same 

 position as when the chitin was being formed. 



The third type of pores is found in the legs of the lady beetle, 

 Epilachna borealis. Instead of the chitin over the external end 

 of the pore being depressed to form a pit, it is elevated dome-like 

 above the surface of the leg. In the center of the dome lies 

 the pore aperture (Fig. 16, PorAp). All the pores in the tro- 

 chanters and most of those in the tibia (Fig. 17, PorAp) are of 

 this type. Sometimes in the tibia is found a pore whose aperture 

 is on a level with the surface of the tibia. The apertures of all 

 the pores in the elytra (Fig. 18, PorAp) and wings (Fig. 19) of 

 this beetle are on a level with the surfaces of the appendages. 

 As already stated, the olfactory pores of beetles are more or 

 less flasklike as a rule, but there are many variations among 



