Brain and Nervous System. 65 



caterpillar, .nearly eight times as many as are found m thj 

 human body. The strength, too, of insects is prodigious. 

 There must be quality in muscles, for muscles as large as 

 those of the elephant and as strong as those of the flea 

 would hardly need the fulcrum which the old philosopher 

 demanded in order to move the world. Fleas have been 

 made to draw miniature cannon, chains and -vagons many 

 hundred times heavier than themselves. 



The nerves of insects are in no wise peculiar, so far as 

 known, except in position. Each nerve consists of a 

 bundle of fibers some of which are sensitive and some 

 motor. As in our bodies, some are knotted, or have gang- 

 lia, and some are not. 



The main nervous cord is double, and has several 

 enlargements (Fig. 16) or ganglia. It runs along the 

 under or ventral side of the body, (Fig. 16), separates 



Fig. 17. 



Brain oj Inseci, ajter Dujardrm 



a a Antennas. 

 000 Ocelli. 



near the head, and after passing around the esophagus, 

 enlarges to form the largest of the ganglia, which serves 

 as a brain (Fig. 17). From the brain many fibers extend 

 on each side to the compound eyes. The minute nerves 

 extend everywhere, and in squeezing out the viscera of an 

 insect, are easily visible. 



In the larva the nerve cord is much as in the adult insect, 

 except the ganglia are more numerous. Girard says, that 

 at first in the larva of the bee there are seventeen ganglia. 

 The supra-sesophageal or brain, three sub-aesophageal, 

 three thoracic — one for each ring— and ten abdominal. 

 Soon the three sub-sesophageal merge into one, as do also 



