1928] Nervous Physiology of Dragon-Fly Larvae 183 
be seen from without. It is located near the base of the labium. 
The brain is visible through the dorsal surface of the head. 
To study the function of various parts of this sytem it is 
only necessary to destroy various parts of it with a needle or a 
fine knife. Moreover, the vitality of the larvae is so great that 
such an operation does not seriously interfere with the vital 
processes. In all of the experiments, larvae four to five centi- 
meters long were used. 
The prothoracic ganglion of a larva was crushed with a 
needle. For half an hour after the operation the insect remained 
motionless. When once it recovered, it could be induced to 
crawl by gently stroking the dorsal surface of its abdomen. The 
first pair of legs, limp and powerless, were not used in the process. 
In the. water the larva moved the mildde and rear legs convul- 
sively and irregularly. The mouth-parts moved when touched. 
Respiratory movements were normal. There was no response 
to visual stimuli. 
The mesothoracic ganglion of a larva was destroyed. After 
the passage of the shock period the first and last pairs of legs 
responded to stimulation. The paralysis of the middle pair of 
legs made crawling practically impossible. Like the preceding 
larva, this one did not respond to visual stimulation. It also 
gave little evidence of volition. 
The metathoracic ganglia of two different larvae were des- 
troyed. Both insects gave evidence of shock, disturbance of 
equilibirum in the water, lack of volition, and inability or disin- 
clination to respond to visual stimuli. Both made some effort to 
crawl. The rear legs were completely incapable of action and 
did not respond to stimuli. In the water the first and second 
pairs of legs moved convulsively. One insect was fairly active; 
the other seemed almost dead. 
The first abdominal ganglion of a larva was destroyed. Al- 
though the respiratory movements were somewhat labored and 
weak after operation, the animal was otherwise quite normal. 
The destruction of the third abdominal ganglion of another 
larva had even less effect than the preceding; the behavior of 
the insect differed in no way from that of a normal animal. 
