122 



THE NERVOUS SYSTEM 



[CH. 



the mouth and oesophagus, and connected with the brain at two 

 points. 



The first three of these are often classed together as the central 

 nervous system. 



In the imaginal Dragonfly, the ventral nerve cord apparently 

 contains only ten pairs of ganglia, though in the larva we can 

 count eleven. This is due to the fact that the first abdominal 

 ganglion moves up into the thorax, and fuses with the metathoracic 

 ganglion posteriorly. The ninth and tenth abdominal segments 

 contain no ganglia ; but the ganglion of the eighth segment is 

 large, and innervates the last three segments. 



The table on p. 120 shews the details of the Central Nervous 

 System in a convenient form. 



vhc 



Fig. 55. Diagram of brain of Austrolestes leda Selys, constructed from transverse 

 sections ( x 20). A. Dorsal view. B. Ventral view, al antennary lobe ; 

 ant antennary nerve; co circumoesophageal commissure; e eye; fc frontal 

 commissure; fg frontal ganglion; ocl lateral ocelli; ocm median ocellus; 

 og optic ganglion; sog suboesophageal ganglion; vnc ventral nerve-cord. 

 Original. 



The Brain (figs. 55, 56, 57). 



The brain is a large mass of nervous matter situated in the 

 head, above the oesophagus, and extending transversely across 

 the whole space between the compound eyes. Its exact position 

 with regard to the head-skeleton has already been explained 



