24 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



II. CHEMORECEPTORS 



Chemoreceptors include both olfactory and gustatory organs. Judg- 

 ing from the anatomy and function of these organs in man and the 

 higher animals, we are not absolutely sure that insects have true 

 chemoreceptors, although their organs certainly belong to the same 

 category. 



I. SO-CALLED OLFACTORY ORGANS 



(a) Antenna!. Organs. — Several investigators have studied the 

 morphology of the antennal organs, but since Schenk's (79) paper 

 is one of the latest and perhaps best, it will suffice for our purpose 

 here. Schenk carefully studied the various types of antennal hairs 

 in both sexes of the following moths: One geometrid {Fidonia 

 piniaria), two bombycids (Orgyia antiqiia and Psyche unicolor), and 

 one zygaenid {Ino pruni). He found five types of sense hairs as 

 follows (see fig. 3 of codling moth) : (i) Pit pegs (Sensilla 

 coeloconica), (2) end pegs (S. styloconica), (3) sense bristles 

 (S. chaetica), (4) sense hairs (S. trichodea), and (5) pegs (S. basi- 

 conica). Relative to the last named only five were found and these on 

 a female of Fidonia. These five types of sense hairs were found on the 

 pectinate or feathered antennae of males and on the filiform or non- 

 feathered ones of the females, and not only on the shafts of both 

 types of antennae but also on all the barbs of the male antennae. The 

 total number of sense hairs found by Schenk in various species is 

 included in table 2, which also gives the tabulated results of the present 

 writer's observations on other species. 



■ A few styles on each antennae do not bear end pegs. 



