VI] THE NERVOUS SYSTEM 135 



nerve-endings in the larva of Aeschna, found that they were all 

 finally connected with the ventral ganglia. Some of these fine 

 endings innervate small sense organs, such as minute sensillae, 

 cones, or tympanulae, on special parts of the cuticle (p. 156). 

 Others end in special enlarged hypoderm-cells, and serve to 

 produce the effect of general sensation over the body-surface. 

 There is no separate peripheral nervous system. 



Physiology of the Nervous System, 



We can only briefly summarize the results obtained by experi- 

 ments upon Dragonflies: 



1. The Brain and Suboesophageal Ganglion control the power 

 of coordination of movement, and almost the whole of the sensory 

 functions of the nervous system. According to Faivre, the brain 

 is the chief seat of sensation, the suboesophageal ganglion alone con- 

 trolling the coordination of movement. A decapitated Dragonfly 

 does not, however, at once lose the power of movement. Large 

 Aeschninae, whose heads have been accidentally struck off with the 

 net, frequently live for as long as two days, and can vigorously 

 flutter their wings, flex their abdomen, or even climb up curtains" 

 by means of their legs. If, however, the head be crushed, the 

 shock causes partial paralysis, from which the insect recovers 

 after the lapse of a time, to lead a feeble existence for a few hours, 

 and then to die. 



2. The Ventral Ganglia. Each of these acts as a motor centre 

 for its own segment, controlling the muscles of that segment. 

 Each is also a very feeble sensory centre, in connection with the 

 peripheral endings of fine sensory nerves mentioned above. The 

 movements of the separate segments are clearly coordinated 

 together. The fact that the effect of a sudden shock is diffuse [6] 

 seems to prove that the power of coordination does not rest entirely 

 with the suboesophageal ganglion. The behaviour of decapitated 

 Dragonflies points in the same direction. 



3. The mechanism of feeding is almost certainly centred 

 entirely in the suboesophageal ganglion. If this ganglion be 

 injured, without damaging the brain, the insect is quite unable 

 to feed. Again, it has been shewn, by at least two competent 



