108 V. G. DETHIER, J. R. LARSEN AND J. R. ADAMS 



CORONAL PEGS IN PITS (PLATE I, FIGS. 1 AND 3) 



These beautifully ornate pegs have not yet been identified with the light 

 microscope, but in electronmicrographs appear in cross section as nearly 

 perfect crowns with projections that usually number twelve. Longitudinal 

 sections reveal that these projections are extensions of the peg wall which 

 proceed outward at right angles to the long axis of the peg but subse- 

 quently bend down to hang parallel to the long axis. Accordingly, cross 

 sections sometimes appear as smooth circles surrounded by a ring of dots. 

 The pegs average 4// in length and 0.5-0.8// in basal diameter. They 

 appear to be innervated by a single neuron, and no perforations have been 

 discerned in their walls. 



THIN-WALLED SURFACE PEGS (PLATE III) 



These pegs average 25// in length and are identical in nearly every 

 respect with the thin-walled pegs found in pits. 



THICK-WALLED SURFACE PEGS 

 (PLATE III, FIGS. 1 AND 3, PLATE IV) 



These, the most common sensilla on the antennae, vary considerably in 

 length. The average length is 83//. The average basal diameter is 8//. 

 All of these taper more than the thin-walled sensilla. Some are straight 

 and acutely pointed while others, usually the longer ones, are gracefully 

 curved. The wall at the base may be from one-quarter to one-half as 

 thick as the diameter of the lumen, but it becomes rapidly thinner as the 

 peg tapers to its tip. 



Each peg is innervated by one to four neurons whose cell bodies lie at a 

 considerable distance beneath the surface. The scolopoid sheath is 

 scalloped to accommodate the various number of dendrites (Plate IV, 

 Figs. 1-4). As in the thin-walled pegs, the dendrites fill the lumen. The 

 walls of the peg also contain the pits already described. 



STELLATE SURFACE PEGS 

 (PLATE III, FIGS. 3-5, PLATE IV, FIG. 5) 



The length of these small pegs is not known since they have been seen 

 only in cross section. The basal diameter is about 1.2//. The peg is 

 characterized by much cuticular fluting and internal cuticular radii which 

 suggest that the scolopoid sheath may extend some distance into the 

 lumen. The structure is best understood by reference to the illustrations. 

 Like the coronal pegs, these are few in number and are unHkely candidates 

 for the function of olfaction. 



DISCUSSION 

 The thick- and thin-walled sensilla on the surface and in the pits are 



