ANATOMY OF THE NERVE CENTRES. 



449 



anterior ventricle is far larger than in the Crayfish ; lastly, a 

 great commissure the commissure of the mesocerebron, or 

 corpus centrale occupies the central cavity, and separates the 

 anterior and middle ventricles. 



FIG. 56. Frontal section of the supra-cesophageal nerve centre of the cockroach 

 (Blatta orientalis] : a, a, antennal (olfactory) ganglia ; c c, corpus centrale ; m, 

 mesocerebron ; m e, external, and m i, internal medullary nucleus of the optic 

 ganglion ; o s, optic peduncle ; tr, trabeculse. 



In the Crickets (Gryllidse), as in the Crustacea and the 

 Cockroach, the infra-oesophageal are separated from the supra- 

 cesophageal ganglia by long nerve-like crura, the cesophageal 



FIG. 57. An oblique section from above and behind, downwards and forwards, 

 through the supra-cesophageal centres of the same insect : cl, cl, the calices ; c, 

 procerebral lobes ; f, corpus fungiforme. The ventricular cavity is seen in front, 

 between the bundles of fibres which support the rudimentary procerebral lobes. 

 The great cells behind the ventricle and between the inner calices are the cells 

 of the pyramidal ganglion. 



connectives, but there is a distinct advance towards the type 

 exhibited by the more specialised Insecta. This is especially 

 seen in the reduction of the proportionate size of the corpora 



302 



