NERVOUS CONTROL OF INSECT MUSCLES 83 



ing prolonged stimulation increases with increasing frequency up to about 

 80 per second. These frequencies are about half the corresponding ones for 

 Periplaneta. The locust prothoracic and mesothoracic extensor tibiae pro- 

 duce final tensions at the tibial tips of barely 0.5 gm., but movement also 

 starts at about 15 per second in the absence of load and increases in rate 

 up to about 150 per second are evident. 



The Mechanism of Transmission 

 Even in the smallest insects, skeletal muscle fibers are seldom less than 

 20/x in diameter and often are as large as lOO/t or even more; this means 

 that the intracellular recording technique can be used in studying trans- 

 mission. With the recent advances in technique a new standard is required 

 in work of this kind, so it seems desirable to lay down the principles which 

 should be follow^ed if the results are to contribute fully as comparative data. 

 They must be regarded as an ideal program rather than as limiting con- 

 ditions. 



Anatomical Features Which Should Be Known 



( 1 ) The nature of the muscle being studied, whether multiple or single 

 unit or diffuse, and whether the units have common or separate inner- 

 vation. 



(2) The number of axons supplying the units being studied ; antidromic 

 stimulation is helpful in determining this. 



(3) The approximate spacing of the end plates along the fibers. 



Stimulation 



( 1 ) Stimulation of separate axons. Where axons are neither separated 

 naturally nor separable by microdissection, difiterences in threshold and 

 conduction velocity should be utilized. 



(2) Monitoring of nerve impulses. Tiny electrodes are particularly sub- 

 ject to polarization and a constant check should be made on the efficacy of 

 stimulation. Monitoring becomes essential when differences in threshold 

 or conduction velocity are being used to study separately axons contained 

 in a common trunk. 



Recording 

 Intracellular recording from as many fibers as possible from all parts 

 of the muscle under consideration. 



The "Fast" System 

 Rijlant (1932) found action potentials associated with vigorous spon- 

 taneous mechanical activity in the legs of Dytiscus and Hydrophilus ; the 

 potentials did not show any facilitation and were probably due to the ac- 



