44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



which the articular membrane, to which the sense fibers are attached, 

 resembles the head of a drum. It was then suggested that these organs 

 might receive stimuli from gusts of wind, weak air currents, or from 

 jars, but the most reasonable function considered was that they regis- 

 rered the movements of the flagellum. 



4. AUDITORY HAIRS 



Years ago there was a controversy as to whether spiders possessed 

 auditory hairs. When a. dead spider was put under a microscope and 

 certain musical tones were produced, some of the hairs on the spider 

 were seen to vibrate. This observation alone is no more proof for an 

 auditory sense in spiders than to say that one stringed musical instru- 

 ment can hear another if a certain cord of the first vibrates when a 

 cord of the second is struck. Recently Minnich (64) has revived the 

 subject of auditory hairs and shows definitely that certain hairs are the 

 sound recej)tors in larvae of the mourning-cloak butterfly. When a 

 test such as was given with a dead spider was repeated, no hairs on 

 a freshly killed larva were seen to respond to the same tones to which 

 larvae normally react. 



Minnich's review shows that certain caterpillars in all instars react 

 to a variety of sounds, including those made by slamming a door, 

 clapping the hands, the human voice, a violin, and a shrill whistle, but 

 the earlier observers did not locate the sound receptors. Minnich used 

 sounds produced by the human voice, piano, organ, violin, dish pan, 

 Galton whistle, tone modulator, and tuning forks. The larvae re- 

 sponded to all of these, except the whistle and modulator, usually b}' 

 throwing the anterior third of the body dorsally or dorsolaterally. The 

 extent of the response to sounds varied with the intensity of the tone. 

 For full-grown larvae the upper limit of response was probably not 

 far from C" (1,024 complete vibrations per second). Responses were 

 obtained from ^2 to 1,024 vibrations per second. Responses to sounds 

 increased greatly with age, being least in the first and greatest in the 

 last two instars. The responsiveness was correlated with the numlDcr 

 of body hairs, which were fewest on the first instar and most abundant 

 on the last instar. Responses to ordinary mechanical stimulation de- 

 creased with age, being greatest in the first and least in the last instar. 

 Headless larvae and fragments of bodies responded to sounds, but the 

 auditory hairs were found to lie chiefly on the anterior two-thirds of 

 the insect. These hairs are probably some of the ordinary tactile ones 

 (Sensilla trichodea) studied by Hilton (34), who claimed that most of 

 the body hairs of caterpillars are innervated. Minnich believes that the 



