42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 8l 



but found them in the larvae of the codHng moth and of Tortrix 

 scrophulariana. 



According to the review by Turner and Schwarz (87), chordotonal 

 organs are not found in Myriapoda and Arachnida. They are found, 

 however, in some insects which do not need a sense of hearing. They 

 are well developed in caterpillars, even in those of Tortricidae, which 

 spend their entire larval period inside of fruit. Eggers (16) remarks 

 that chordotonal organs have been found in the first antennal segment 

 (scape) of Apterygota, Orthoptera, and Hemiptera; in the second 

 antennal segment (pedicel) of Neuroptera ; and in the third antennal 

 segment (first segment of funiculus) of Orthoptera. Some of these 

 are called the Johnston organs, which are discussed later. 



In the bases of lepidopterous wings Vogel (89) distinguished two 

 types of sense receptors — chordotonal organs (fig. 13, C, Ch) and 

 " Sinneskuppeln " (P) or olfactory pores. The former (fig. 13, D) 

 seem to be true chordotonal organs, but the present writer did not 

 see them in codling-moth wings or in those of other Lepidoptera. 



Nothing definite is known about the function of the chordotonal 

 organs, but they are usually considered as sound receptors. Since 

 most of the movements of insects result in rhythms, as pointed out 

 by Eggers, Snodgrass (81) suggests that these organs be regarded 

 as rhythmometers. 



3. JOHNSTON ORGANS 



Tympanic organs, chordotonal organs, and Johnston organs are all 

 chordotonal organs, because each sense element is chordlike in shape 

 and has a sense rod, scolopala, or " Stiff " according to the Germans. 

 A tympanic organ is quite dififerent from the other two types owing 

 to the presence of a drum head or tympanum, A chordontonal organ 

 and a Johnston organ usually differ little; if found in the pedicel, 

 it is generally considered the latter ; if found elsewhere, it is called the 

 former ; but in many insects both occur in the pedicel, A good review 

 on this subject is by Snodgrass (81). The paper by Eggers (16) is 

 the most comprehensive on this subject. He studied the Johnston 

 organs in the pedicels of most of the insect orders and concluded that 

 they are true '' Stift " organs and are common to all insects, including 

 Apterygota. In regard to the antennae of larvae he found them in 

 hemimetabolous forms, but absent in holometabolous ones. Therefore, 

 caterpillars do not have the Johnston organs. 



In both sexes of the codling moth the present writer found the 

 Johnston organs (fig. 14) to be highly developed, and the sense rod 



