128 



INVERTEBRATE PHYSIOLOGY 



secondary elements of the articulation is shown in Fig. 5C, taken on the 

 same animal as records A and B. Sensory elements of the base of the wing 

 which regulate loading in the articulation may have been injured. In one 

 case the articulation was placed into a unique state by CCI4 (Fig. 5D) ; for, 

 after a delay on the up stroke, the critical point was passed but the moving 

 parts apparently hit an elastic stop, rebounding back past the critical 

 point immediately, without locking into the up position. The mechanical 

 action here is similar to that which accounts for the ringing of the tymbal 

 in the cicadas studied by Pringle ( 1954) . 



To complete this survey of the kinds of movements that may be brought 

 about by the vmique mechanical system and its equally unique driving 

 muscles, a few normal starts and stops are illustrated in the records of 

 Fig. 6. In A the fly was making a series of starts and stops but there was 



A 



I I I 



Fig. 6. Scutellar movements during starts and stops recorded on fly, Sarcophaga 

 bullata, with optical levers. A, normal ; B, wings removed ; C, wings loaded with wax. 

 Time scale applies to all records. 



Still evidence of a continuous rhythm of very small amplitude between one 

 stop and the next start. The articulation is set very rapidly in a normal 

 start, for full amplitude is attained almost immediately. The slight vibra- 

 tions in the record suggest that the indirect fibrillar muscles are excited 

 before the articulation is set. A stop with wings removed, B, is contrasted 



