102 INVERTEBRATE PHYSIOLOGY 



The Evolution of the Myogenic Property 

 OF Insect Fibrillar Muscle 



Boettiger (this symposium) has evidence that the myogenic type of 

 flight motor occurs in Diptera, Hymenoptera, and Coleoptera and in the 

 smaller Homoptera (but not in cicada flight muscle) ; it also occurs in the 

 tymbal muscle of cicadas of the genus Platypleura. The flight muscles of 

 other insects show the normal 1 :1 ratio between nerve impulses and muscu- 

 lar contractions (Roeder 1951). Hagiwara, Uchiyama, and Watanabe 

 ( 1954) and Hagiwara ( 1956) have shown that a 1 :1 system occurs in the 

 tymbal muscles of certain cicadas, and in a survey of some of the larger 

 Japanese species they have found the fully developed myogenic system only 

 in Platypleura kaeuipjeri. In my paper on the physiology of sound produc- 

 tion (Pringle, 1954b), I suggested that the tymbal muscle might be an 

 evolutionary development of the metathoracic flight muscles, but I have 

 more recently made a detailed investigation of the anatomy of the sound- 

 production system in the Homoptera Auchenorrhyncha (Pringle, 1956) 

 and am forced to revise this opinion. There is a primitive genus of cicadas, 

 Tettigarcta, the two species of w4iich are found in the mountains of Aus- 

 tralia, and I have been able to obtain well-preserved specimens of both 

 sexes of each species. In the anatomy of its sound-production system, 

 Tettigarcta is intermediate between true cicadas and cercopids, which 

 have been well discribed by Ossiannilsson (1949). The whole sound-pro- 

 duction system appears to be morphologically in the first abdominal seg- 

 ment, as correctly stated by Myers ( 1928) ; and I have now concluded that 

 sound production has evolved not from the flight system but from a move- 

 ment made during copulation, which has become converted into a noncon- 

 tact communication system by the development first of a click system in the 

 first abdominal tergum (cercopids and Tettigarcta) and then by the 

 addition of a sound-frequency carrier as the damping of the clicks is re- 

 duced by the presence of internal resonant air sacs (true cicadas). There 

 is a correlated development of the receptor organ in these insects, Tetti- 

 garcta having chordotonal organs, probably sensitive to the click vibrations, 

 in the same morphological position as the tympanal chordotonal organs of 

 true cicadas. 



This re-interpretation of the homologies, coupled with Hagiwara's evi- 

 dence that the myogenic system is present in the tymbal muscles of only 

 some cicada genera, makes it clear that the development of the myogenic 

 rhythm property in connection with sound production is an independent 

 evolution from its appearance in the flight motor system. Probably here 

 also it has evolved independently in the four insect orders in which it 

 occurs. This at once poses two questions : 



