MACHINERY OF INSECT FLIGHT 119 



Lamellar muscle is found in Odonata and certain Orthoptera ( Blattidae, 

 Mantidae) which do not have typical longitudinal muscles attached to a 

 well-developed phragma. This muscle type apparently appeared early in the 

 insects. In many softer-bodied insects, as the Lepidoptera, and in those with 

 two sets of longitudinal muscles, as the Ephemeroptera and Locustidae, 

 microfibrillar muscle is found. The insects with the most spectacular flight 

 ability have harder cuticles and fibrillar muscle (Hymenoptera, Diptera, 

 Coleoptera, Hemiptera, and many Homoptera). 



The present evidence supports the idea that two very dififerent flight 

 mechanisms have evolved among the insects, one associated with presence 

 of microfibrillar or lamellar muscles and one with fibrillar muscle. In the 

 former type, little is known of the mechanical aspects of flight or of the 

 physiology of the driving muscles. Where studies have been made (Roeder, 

 1951 ) , it is evident that the wing stroke is synchronous with nerve stimula- 

 tion of the muscle. This stimulation is often a single impulse but may be 

 multiple (McCann, unpublished). The flight muscles show little summa- 

 tion and each stroke is either a twitch or brief tetanus. This mechanism we 

 have termed the synchronous type. 



The existence in insects of some sort of peripheral control of wing move- 

 ment was suggested by the experiments of de Geer ( 1776), who found that 

 on removing the wings of some insects, thereby unloading the muscles, 

 the wing beat frequency greatly increased. Pringle (1949) demonstrated 

 that the action potentials appearing in the thorax of flies during flight were 

 not correlated with the wing movements. By simultaneous recording of 

 these potentials and of thoracic movements, Roeder (1951) confirmed 

 this observation for several species of Diptera and Hymenoptera. More 

 recently this behavior has been found in Coleoptera, Homoptera, and 

 Hemiptera. This second t}'pe of flight mechanism we term asynochronous. 



Only in the Homoptera is there evidence for the existence of both syn- 

 chronous and asynchronous types in one order. The extensive study of 

 this group by Tiegs (1955) suggests a step in the evolution of the asyn- 

 chronous mechanism. He finds that in the cicadas the synchronous flight 

 muscle arises by the multiplication of a few rudimentary muscle fibers. In 

 the other Homoptera studied, formerly free myoblasts become incorporated 

 into the young fibers. The myoblasts extend along the growing fiber, add- 

 ing new fibrils. In jassids each myoblast adds one new fibril. In cercopids 

 the muscle starts to develop by cleavage of functional nymphal fibers or of 

 rudimentary fibers arising in the early instars. Then the free myoblasts 

 become incorporated into these young fibers. 



With this information it is tempting to speculate that it is only from the 

 free myoblasts that fibrillar muscle can be formed. The apparent presence 

 of both mechanisms in the cercopids might then result from the fact that 



