OLFACTORY ORGANS OF A COLEOPTEROUS LARVA 



127 



its larva are about equally developed, and we are safe in assuming 

 that the adult smells well, because many species of beetles have 

 been tested with odors (see the writer's paper on the olfactory 

 sens? of insects, 1914c). 



To see how well the tip of an antenna is provided with olfactory 

 organs, the reader is referred to figure 30, which shows in longi- 

 tudinal section 5 compound organs (PI) and 2 single olfactory 

 organs (Por). Attention is called to the fan-shaped bunches of 

 sense cells {SC) and to the manner in which the nerve sends off 

 branches (NB) ; in cross sections these branches appear as shown 



in figure 15. 



/ 



Fig. 30. Longitudinal section of tip of antenna, showing internal structure 

 and innervation of compound (PI) and single olfactory organs (Por), and tactile 

 hair (THr); two-thirds diagrammatic, X 100. At this magnification the pore 

 apertures are never discernible. Sense cell group (SC), nerve branch (NB), and 

 trachea (Tr). 



' THE OLFACTORY PEGS 



Short, stubby hairs, known as olfactory pegs, are common on 

 the antennae and mouth parts of most adult insects. They may 

 or may not arise from pits, but are always innervated. Since 

 their tips are covered with hard chitin, they certainly can not 

 serve as olfactory organs, although they are well adapted for 

 tactile purposes. 



While hairs are common to all the antennal segments of adul't 

 insects, they were formed on only the first and last antennal 

 segments of the larva under discussion. The only hairs present 



