INSECTS
Fig. 71. The nervous system of the head of a grasshopper, as seen by removal of the facial wall
AntNv, antennal nerve; 1Br, 2Br, 3Br, the three parts of the brain; CoeCon, circumoesophageal connectives; 3Com, suboesophageal commissure of the third lobes of the brain; FrGng, frontal ganglion; FrCon, frontal ganglion connective with the brain; LbNv, labial nerve; LmNv, labral nerve; MdNv mandibular nerve; MxNv, maxillary nerve; O, simple eye; OpL, optic lobe connected with the brain; RNv, recurrent nerve; SoeGng, suboesophageal ganglion
lying against the lower wall of the first body segment (Fig. 72, Gng 1), which is likewise connected with a fourth mass in the second segment, and so on. The central nervous system of the insect thus consists of a series of small nerve masses united by double nerve cords. The nerve masses are known as ganglia (Gng), and the uniting cords are called the connectives (Fig. 71, Con). Typically there is a ganglion for each of the first eleven body segments, besides the brain and the lower ganglion of the head.
The brain of an insect (Fig. 71) has a highly complex internal structure, but it is a less important controlling center than is the brain of a vertebrate animal. The other ganglia have much independence of function, each giving the stimuli for movements of its own segment. For this
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