124 



THE NERVOUS SYSTEM 



[CH. 



body in the Dragonfly's brain is small, and forms merely a thick 

 mass of transverse nerve-fibres enclosing a few small groups of 



P.I D. 



C. 



Fig. 56. T.S. through region of brain of Austrolestes leda Selys ( x 41). The numbers 

 give the order, from before backwards, out of a total of 200 sections of the 

 whole head. A (No. 88). Frontal ganglion. B (No. 103). Deuto- and trito- 

 cerebrum. c (No. 108). Protocerebrum (anterior part) and suboesophageal 

 ganglion. D (No. 127). Protocerebrum, median ocellus and optic nerve. 

 E (No. 130). The same, further back. F (No. 135). The same, with calyx 

 (cal). G (No. 138). The same, with nerves to lateral ocelli, br bridge of 

 procerebral lobes; cal calyx; cb central body; Ibn labial nerve; mb giant 

 cells of mushroom body ; od lateral ocellus ; ocln nerves to same ; ocm median 

 ocellus; ocn nerves to same; oel oesophageal lobe; oes oesophagus; op optic 

 nerve; ot optic tubercle; pi piocerebrol lobe; tc commissure of the sub- 

 oesophageal ring ; tr, tr' tracheae. Other references as in fig. 55. Original. 



