Figure 65 gives a view of one side of the supra-oesophageal ganglion of the worker of an ant,—_Formica rufa_,—and is taken from Leydig, who gives the following elucidation of it: _A_, primary lobe, _a_, homogeneous granular inner substance, _b_, cellular envelope; _B_, stalked bodies (gyri cerebrales), _a_, _b_, as before; _C_, presumed olfactory lobes, _c_, inner substance, _d_, ganglionic masses; _D_, ocular lobes, _e_, _f_, _g_, _h_, various layers of the same; _E_, origin of lateral commissures; _F_, median commissure in interior of brain; _G_, lower brain (sub-oesophageal ganglion); _H_, ocelli; _J_, faceted eye. [Illustration: FIG. 66.—Stomato-gastric nerves of Cockroach: A, with brain _in situ_, after Koestler; B, with the brain removed, after Miall and Denny: _s.g_, supra-oesophageal ganglion; _o_, optic nerve; _a_, antennary nerve; _f.g_, frontal ganglion; _oe_, oesophagus; _c_, connective; _p.g_, paired ganglia; _v.g_, crop or ventricular ganglion; _r_, recurrent nerve.] Besides the brain and the great chain of ganglia there exists an accessory system, or systems, sometimes called the sympathetic, vagus, or visceral system. Although complex, these parts are delicate and difficult of dissection, and are consequently not so well known as is the ganglionic chain. There is a connecting or median nerve cord, communicating with the longitudinal commissures of each segment, and itself dilating into ganglia at intervals; this is sometimes called the unpaired system. There is another group of nerves having paired ganglia, {121}starting from a small ganglion in the forehead, then connecting with the brain, and afterwards extending along the oesophagus to the crop and proventriculus (Fig. 66). This is usually called the stomatogastric system. The oesophageal ring we have already spoken of. By means of these accessory nervous systems all the organs of the body are brought into more or less direct relation with the brain and the ganglionic chain. Our knowledge of these subsidiary nervous systems is by no means extensive, and their nomenclature is very unsettled; little is actually known as to their functions. ORGANS OF SENSE.