ANATOMY OF INSECTS INTERNAL 



37 



The work performed by the muscles of insects appears prodigious 

 compared with that done by higher animals. Thus the weakest 

 insect can pull over twenty times its weight. A house-fly can 

 carry a match, to equal which a man would need to carry a timber 

 thirty-five feet long and as large around as his body. An earwig can 

 lift twelve times its weight, and a honey-bee, in flight, carries four 

 fifths of its weight. A small insect is relatively stronger than a large 

 one, and the relative strength of insects is largely accounted for by 

 their small size. This is due to the fact that the weight increases as 

 the cube of a single 

 dimension, while the 

 strength of a muscle 

 increases as the square 

 of its diameter. The 

 endurance and rapidity 

 of muscular action of 

 insects is no less mar- 

 velous. By determin- 

 ing the pitch of the 

 note made by the wing 

 vibrations of a gnat, 

 physicists have shown 

 that its wings may move 

 as many as fifteen thou- 

 sand times per minute. 



FIG. 42. Nervous system of honey-bee, at a, and 



of its larva, at b, showing the simple type of the 



larva and the specialization in the adult due to 



fusion of the ganglia 



The prolonged vibra- 

 tion of the honey-bee's 

 wings is another instance of remarkable muscular endurance. 



Nervous system. The nervous system consists of a series of 

 small white ganglia which are connected by a double nerve cord 

 lying along the bottom of the body cavity. In the larvae there is 

 usually one ganglion to each segment, but in the adult insects 

 the ganglia are often fused together, those of the thorax and an- 

 terior abdominal segments having grown together, as well as those 

 toward the tip of the abdomen. In the head the ganglia have 

 grown together to form the brain, which lies just above the esoph- 

 agus and which is connected with the subesophageal ganglion by 

 a double nerve cord, one commissure of which passes on either side 



