VI] 



THE NERVOUS SYSTEM 



133 



to the segmental muscles of these three segments respectively. 

 A strong branch from each of the first pair (eighth segment nerves, 

 w g ) runs forward along the heart. A branch from each of the last 

 pair (tenth segment nerves, w 10 ) passes to the appendages. A fourth 

 pair of strong nerves, placed anteriorly to the above-mentioned 

 three pairs, supplies the reproductive organs. These are called 

 the genital nerves (rri). 



The thoracic and abdominal ganglia are closely similar in 

 structure. Each is seen, in transverse section, to be clearly 

 compounded of two fused ganglionic masses, placed side by side, 

 and closely fused along the median vertical plane. The nerve-cells 

 in all cases lie chiefly ventrally, the nerve-fibres chiefly dorsally. 

 The nerve-cells are unipolar, and the 

 cords are formed from their united 

 prolongations or fibres. 



The ventral nerve-cord of the 

 newly-hatched larva (fig. 59) is very 

 different from that of the imago. 

 Relatively to the size of the animal, 

 the ganglia are here immense, while 

 the nerve-cords are almost non-existent. 

 In most Libellulidae, the ganglia actu- 

 ally touch one another like a row of 

 flat beads. At each instar, the nerve- 

 cords lengthen slightly, while the 

 ganglia do not appear to increase to 

 any appreciable extent. Hence the 

 ventral chain becomes gradually at- 

 tenuated, and the ganglia smaller and 

 smaller by comparison with the sizes of 

 their segments. 



Fig. 59. Nervous system of 

 newly-hatched larva of Dip- 

 lacodes haematodes Burm. 

 (x 53). References as in 

 fig. 54. Original, stained 

 preparation 



The Sympathetic Nervous System (fig. 60). 



The presence of a complex and well-developed sympathetic 

 nervous system in the Dragonfly was demonstrated by Brandt [15], 

 whose work still remains the chief source of our knowledge of 



