THE COCKROACH : 



The nervous centres of the head form a thick, irregular ring, 

 which swells above and below into ganglionic enlargements, 

 and leaves only a small central opening, occupied by the 

 oesophagus. The tentorium separates the brain or supra- 

 cesophageal ganglion from the sub-cesophageal, while the 

 connectives traverse its central plate. Since the oesophagus 

 passes above the plate, the investing nervous ring also lies 

 almost wholly above the tentorium. 



Fig. 40. Side view of Brain of Cockroach, X 25. op, optic nerve; oe, oesophagus; 

 t, tentorium; sb, sub-oesophageal ganglion; mn, mx, mx', nerves to mandible 

 and maxillae. Copied from E. T. Newton. 



The brain is small in comparison with the whole head ; it 

 consists of two rounded lateral masses or hemispheres, incom- 

 pletely divided by a deep and narrow median fissure. Large 

 optic nerves are given off laterally from the upper part of each 

 hemisphere ; lower down, and on the front of the brain, are the 

 two gently rounded antennary lobes, from each of which 

 proceeds an antennary nerve ; while from the front and upper 

 part of each hemisphere a small nerve passes to the so-called 

 "ocellus/' a transparent spot lying internal to the antennary 



