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INVERTEBRATE PHYSIOLOGY 



duced action and resting potentials similar to that found in beetles, though 

 usually smaller. Qualitatively it appears that the electrical manifestation 

 of the excitatory processes of fibrillar muscle fibers are similar to those of 

 ether muscles. Different groups of insects have fibrillar muscle with quanti- 

 tatively difterent electrical properties. These variations may eventually be 

 correlated with the different patterns of nerve innervation of fibrillar 

 muscles indicated by the work of Tiegs ( 1955) . 



n o V e. m e riir 



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ec. 



Fig. 7. Action potentials of the indirect flight muscles of the fly, Sarcophaga bul- 

 lata. A, Normal discharge recorded with external leads ; B, during stimulation of 

 the ganglion, the action potentials of all fibers recruited to stimulus frequency, flight 

 continuing ; C, same after cessation of flight movements. Time scale applies to records 

 A, B, and C. D, single-fiber action potential of longitudinal flight muscle recorded 

 with internal microelectrode on stimulation through leads directly on the muscle; 

 + and — refer to the sign of the internal electrode. Stimulus artifact shows at the 

 beginning of the record. E, single-fiber action potentials recorded with internal elec- 

 trode during spontaneous flight movement compared with thoracic movements. Small 

 movements in the action potential record are probably action potentials in adjacent 

 fibers. 



When transmeml)rane potentials of a muscle fiber are recorded during 

 flight, one observes a beautifully regular discharge, apparently in all fibers. 

 Identical discharge patterns can be elicited by the vapors of ether and a 

 number of other compounds. With CCI4 the discharge frequency rises 



