NO. lO TROPISMS OF LEPIDOPTERA McINDOO 4I 



I. TYMPANIC ORGANS 



According to Eltringham's (19) review, tympanic organs in Lepi- 

 doptera were first recorded in 1889 in Uraniidae. Since that date 

 several other writers have described these sense organs in Lepidoptera, 

 which are similar in strncture and probably in function to those in 

 Orthoptera. As Eggers (15) has presented the most comprehensive 

 paper on this subject, his results are here briefly summarized. In all 

 he examined 150 species of moths and 5 species of butterflies, repre- 

 senting over 40 families. No tympanic organs were found in 39 

 species of moths and in the five species of butterflies. They were 

 found, however, in various stages of development in the thorax of 

 95 species and in the abdomen of 16 species of the moths. Thus 

 71.6 per cent of all had tympanic organs. Judging from this study 

 butterflies and many moths, including Sphingidae, Saturniidae, and 

 Bombycidae, apparently have no tympanic organs, and none was found 

 in the codling moth by the present writer. The location and structure 

 of the organs found by Eggers are represented by figure 13, A and B. 



Eggers (17) next determined that the tympanic organs in noctuid 

 moths are auditory in function. Noctuids, when in an excited condi- 

 tion, reacted to difl:'erent sounds by flying or by raising the wings. 

 They were tested under glass funnels to loud, sharp sounds such as 

 those made by hand clapping, and to soft ones, as the twisting of a 

 glass stopper in a bottle. When the drum heads (fig. 13, A, T) of 

 both of the tympanic organs were destroyed the moths no longer 

 reacted to sounds. When the drum head in one organ was destroyed 

 the moths reacted to sounds in seven-tenths of the cases by flying. 

 Moths with intact tympanic organs but with wings removed reacted 

 to sounds in one-half the cases by running; in the other cases, by 

 quick movements of the leg or antennae. Moths with intact tympanic 

 organs but with antennae removed, reacted to sounds by flying. He 

 concluded that these organs are sound receptors, analogous to the ears 

 of mammals. 



2. CHORDOTONAL ORGANS 



The name chordotonal means a chord, or string, which is sensitive 

 to tones. Graber (26) in 1882 presented the first comprehensive paper 

 on the chordotonal organs, and much of our present information on 

 this subject is based solely on his report. He apparently found these 

 organs in a wide range of adult and larval insects, but he evidently 

 included other sense organs too. Excluding the olfactory pores on 

 insect wings, he did not find chordotonal organs in adult Lepidoptera, 



