NO. 1 8 



SENSE ORGANS OF COLEOPTERA — McINDOO 



45 



when present, are considered the olfactory organs by most writers. 

 Figure 7 illustrates the antennal organs of a water beetle, copied from 

 Hochreuther (25). The pore plates {PP), hollow pit pegs (HPPg), 

 and massive pit pegs (MPPg) might be called olfactory organs, but 

 Hochreuther regarded only the hollow pit pegs as probably olfactory 

 in function. If they really act as olfactory organs, then the mouth 

 parts, thorax, legs, and sexual organs must aid in receiving odor 

 stimuli, because Hochreuther found them also on these parts of the 

 anatomy. 



Fig. 6. — Drawings of antennae of adult Mexican bean beetle, showing organs 

 on them. A, ventral surface, and B, dorsal surface, showing location of follow- 

 ing: Hr, noninnervated hairs; /, Johnston organs: P, pores called olfactory 

 by the writer ; OHr, so-called olfactory hairs ; and St, tactile hairs. C, a semi- 

 diagrammatic drawing from a section through tenth segment, showing structure 

 of so-called olfactory hairs (OHr) and their sense cells (SC). A and B, X 53; 

 and C, X 500. 



(b) olfactory pores 



The writer (46, p. 1105) in 1926 cited references pertaining to 

 these organs in beetles and in 1929 he (47, p. 27) stated why they 

 were called "olfactory pores." In 1915 (41) he made a comparative 

 study of them in 50 species of beetles belonging to 47 genera and rep- 

 resenting 34 families. In that study only the legs, elytra, and wings 

 were examined for these pores. A group of pores (fig. 8, A and B, j) 

 was always found on the peduncle of each elytron. The number of 

 pores in it ranged from 12 to 310, and the more pores in the group 

 the smaller they were and the closer they were together. Of the 47 



