OLFACTORY ORGANS OF A COLEOPTEROUS LARVA 



121 



inside the pore wall is much lighter in color than elsewhere, and 

 at its center lies a minute transparent spot, the pore aperture 

 (PorAp), whose diameter is diminished by focusing downward; 

 this shows that the pore aperture is funnel-shaped. 



b. Compound olfactory organs. For a general view of the plates 

 belonging to these organs, the reader is referred to figures 23 to 

 25. These plates are variously shaped, but the oblong ones, as 

 will be shown later, are the most common. Attention is called 



-TH^ 



■'^ii'i'in 





PorB / PofW 



16 



15 



^^ 



^ 



20 



\ 



21 



Figs. 16 to 22. External view of single olfactory organs and hairs, X 320. 

 Fig. 16 represents 4 organs from trochanter, showing pore border (PorB), pore 

 aperture (PorAp), and pore wall (PorW); fig. 17, 2 organs and a hair from hypo- 

 pleural region; fig. 18, 2 organs from maxilla; fig. 19, 2 organs and a hair from dorsal 

 surface of labrum; fig. 20, 2 organs from labium; fig. 21, 2 organs and a hair from . 

 epicranium; and fig. 22, a hair from first antennal segment. 



to the dark borders around the plates and to the many minute 

 circles, the pore apertures, inside the borders. 



Figures 23 and 24 are from opposite sides of the tip of the same 

 antenna, viewed from flat surfaces, and figure 25 is the enlarge- 

 ment of the largest plate shown in figure 24. Attention is called 

 to the great variation in size of these plates; on other antennae, 

 however, the variation is even greater. It will be noted that each 

 plate has an inside, rather than an outside border and that each 

 one bears many pore apertures having diameters about equal to 

 those of the single olfactory organs. 



