22 The Structure and Special Physiology of Insects 
Fig. 42. Fig. 43. 
Fig. 42. —Diagram of ventral nerve-cord of locust, Dissosteira Carolina . (After Snod¬ 
grass; twice natural size.) 
Fig. 43. —Diagram of the nervous system of the house-fly. (After Brandt; much 
enlarged.) 
Fig. 44. —Nervous system of a midge, Chironomus sp. (After Brandt, much enlarged.) 
commissures are in most insects more or less fused to form single ganglia 
and a single commissure, but in others the commissures, 
at least, are quite distinct. In the simpler or more 
generalized condition of the nervous system as seen 
in the simpler insects and the larvae of the higher 
ones there are from three or four to seven or eight 
abdominal ganglion pairs, one pair to a segment, a 
pair in each of the three thoracic segments, and one 
in the head just under the oesophagus. From this 
ganglion (or fused pair) circumoesophageal commis¬ 
sures run up around the oesophagus to an important 
ganglion (also composed of the fused members of a 
pair) lying just above the oesophagus and called the 
brain, or supraoesophageal ganglion (Figs. 45, 46, and 
47). From this proceed the nerves to those impor¬ 
tant organs of special sense situated on the head, the 
antennae and eyes. From the suboesophageal gan¬ 
glion nerves run to the mouth-parts, from the thoracic ganglia to the 
Fig. 45. —Brain, com¬ 
pound eyes, and part 
of sympathetic nerv¬ 
ous system of locust, 
Dissosteira Carolina. 
(After Snodgrass; 
greatly magnified.) 
