HEXAPODA. 



73 



already indicated, consists of a ganglion in the head above the oesoph- 

 agus, and of a series of ganglia, typically one for each segment of 

 the body, lying on the floor of the body cav- 

 ity, and connected by two longitudinal cords. 

 In the head, one of these cords passes on 

 each side of the oesophagus, from the brain 

 to another ganglion in the head below the 

 oesophagus, thus forming a nervous collar 

 about the alimentary canal. From each 

 ganglion nerves arise, which supply the ad- 

 jacent parts; and from the thoracic ganglia 

 nerves extend to the legs and wings. This 

 series of ganglia is really a double one; but 

 each pair of ganglia are more or less closely 

 united on the middle line of the body, and 

 often appear as a single ganglion. Figure 84 

 gives a general view of the nervous system of 

 Corydalis cornuta. From the brain (a) two 

 large nerves extend to the compound eyes, 

 and a smaller pair to the antennae , the sub- 

 cesophageal ganglion (/>) supplies the mouth- 

 parts with nerves ; and each of the thoracic 

 and abdominal ganglia supplies its segment 

 of the body. 



How Insects Breathe The Respiratory System. A common mis- 

 take made by beginners in the study of Entomology is to suppose 

 that insects breathe through the mouth as do the higher animals. 

 Many a beginner has carefully poured chloroform on the head of an 

 insect in the expectation of killing it in that way, and has been sur- 

 prised at his poor success. 



The truth is, insects breathe through their sides. If an insect be 

 carefully examined, there can be found along the sides of the body a 

 series of openings (Fig. 85). These are the openings through which 



FIG. 84. Nervous system of 

 Corydalis. (After Leidy.) 



FIG. 85. Side-view of Locust with wings removed. 



the air passes into the respiratory system and are termed spiracles 

 (spir'a-cles). 



