56 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



A. The transparent plate (PI) is bordered by tiny pseudo-hairs (PH) 

 and the hypodermis (B, Hyp) just beneath the plate is very thick. 

 Each hair is connected with a sense cell (SC) and these cells almost 

 fill the lumen of the segment. The sense cells are very long and 

 slender and have conspicuous nuclei. 



Now, if aqueous solutions can pass quickly through the walls of these 

 sense hairs in order to stimulate the nerves inside, these structures 

 would be excellent taste organs. Or, if air can pass quickly to the 

 nerves, they would then be olfactory organs. The fact that the bean 

 beetle possesses two of these highly developed sense organs helps 

 to explain how these insects were able to distinguish so readily between 

 the various aqueous solutions and insecticides fed to them. 



III. AUDIRFXEPTORS 



Since the writer (46, p. 11 19; 47, p. 39) has already reviewed the 

 literature on the sense of hearing in insects, no further review is 

 necessary here, other than to cite the recent book by Eggers(i4). 



I. JOHNSTON ORGANS 



In caustic-potash preparations of the antennae of the adult bean 

 beetle the location of the Johnston organs may be determined by 

 focusing downward with the microscope when looking at the distal 

 end of the second antennal segment. A serrated structure (fig. 6, A 

 and B, /) will be observed to encircle the segment. The distal ends 

 of the sense cells are attached to this structure. In longitudinal sec- 

 tions the Johnston organs appear about as shown in figure i8, A. At 

 the base of the second segment the nerve divides into two branches, 

 which run directly to the sense cells (SC). Formerly the Johnston 

 organs were assumed to be auditory in function, but more recently 

 they have been called muscular receptors or statical-dynamic organs 

 to register the movements of the antennae. 



2. CHORDOTONAL ORGANS 



Chordotonal organs very often accompany the Johnston organs, 

 as illustrated by the writer in the cotton boll weevil ; but none was 

 found in the Mexican bean beetle. Many sections through the larvae 

 were also made and studied, but no chordotonal or Johnston organs 

 were found. 



Since the writer has never reviewed the literature on the so-called 

 auditory organs in larvae, the reader is referred to the paper by Hess 

 (24) who gives a brief history of the chordotonal organs and de- 



