10 GENEBAL ZOOLOGY 



casting of the skin (molting) may be an act of excretion of 

 considerable importance. 



The Nervous System. All the processes just described, 

 even the flow of blood and the secretion (formation) of the 

 digestive fluids, are under the control of the nervous system. 

 Through its organs of sense the locust is brought into touch 

 with the outside world ; by its control over the muscles, move- 

 ments are made. The nervous system of the locust consists 

 of a series of connected nerve centers, called ganglia (Fig. 3, 

 24, 28, 29), from which nerves are given off to the different 

 parts of the body. There are two kinds of nerves, sensory and 

 motor; the former carry messages from the various sense- 

 organs to the ganglia ; the latter carry impulses from the 

 ganglia, which result in the contraction of muscles and move- 

 ments of the various organs, or of the body as a whole. 



The largest ganglion is in the head, and is generally called 

 the " brain," or, because of its position just above the oesoph- 

 agus, the supraoesophageal ganglion (Fig. 3, 24). From this 

 ganglion pass the nerves which go to the eyes, antennae, 

 and labrum. Two cords encircling the oesophagus pass to the 

 next ganglion, which, owing to its position just beneath the 

 oesophagus, is called the suboesopliageal ganglion (Fig. 3, 28). 

 This ganglion sends nerves to the mandibles and maxillse. 

 Both the supraoesophageal and the suboesophageal ganglia 

 are the seat of will in the locust, and preside over and 

 coordinate the various general movements of the locust's body. 

 It has been shown that an insect may live for months with 

 the anterior of these ganglia destroyed, if the other is not 

 injured. The insect will feed if food is placed to its mouth, 

 but it loses the power to go in search of food. Of the other 

 ganglia three are in the thorax and five are in the abdomen, 

 forming a median chain resting on the ventral surface of the 

 body-cavity. These ganglia are centers for movements and 

 respiration in the somites to which they belong. 



