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. 
Pd 
fs ‘ 
Fic. 56.—Frontal section of the supra-cesophageal nerve centre of the cockroach 
(Blatta orientalis): a, a, antennal (olfactory) ganglia; ¢ c, corpus centrale; , 
mesocerebron ; z e, external, and 7 2, internal medullary nucleus of the optic 
ganglion ; 0 s, optic peduncle ; ¢, trabecule. 
In the Crickets (Gryllide), as in the Crustacea and the 
Cockroach, the infra-cesophageal are separated from the supra- 
cesophageal ganglia by long nerve-like crura, the cesophageal 
IG. 57.—An oblique section from above and behind, downwards and forwards, 
through the supra-cesophageal centres of the same insect: ¢/, c/, the calices ; a 
procerebral lobes ; /, 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 
30—2 
