THE INTERNAL ANATOMY OF INSECTS 



127 



aorta and the oesophagus, to terminate in the ventricular ganghon; 

 the ventricular ganglion (v) , this is a minute ganghon on the middle 

 line, a short distance cauda of the brain, and between the aorta and 

 the oesophagus; and the stomogastric nerves (st), these are two nerves 

 which extend back from the caudal border of the ventricular ganglion, 

 they are parallel for a short distance, then they separate and pass, one 

 on each side, to the sides of the alimentary canal which they follow 

 to the proventriculus. 



The paired division of the oesophageal sympathetic nervous system 

 varies greatly in form in different insects. In the larv^a of Corydalus, 

 there is a single pair of ganglia (Fig. 142 and 143, Ig), one on each 

 side of the oesophagus; each of these ganglia is connected with the 

 brain b}^ two nerves {m and u) but they are not connected with each 



other nor with the unpaired division 

 of this system. In a cockroach 

 (Fig. 144), there are two pairs of 

 ganglia {ag and pg); the two ganglia 

 of each side are connected with each 

 \ other and with the recurrent nerve of 

 the unpaired division. 



As yet comparatively little is 

 known regarding the function of the 

 oesophageal sjnnpathetic nervous sys- 

 tem of insects ; ner\^es extending from 

 it have been traced to the clypeus, 

 the muscles of the pharynx, the oeso- 

 phagus, the mid-intestine, the salivary 

 glands, the aorta, and the heart. 

 Its function is probably analogous to 

 that of the sympathetic nervous sys- 

 tem of Vertebrates. 



Fig. 144. — The cesophageal sympa- 

 thetic nervous system of Peri- 

 planeta orientalis; the outHnes of 

 the brain (6) and the roots of the 

 antennal nerve which cover a por- 

 tion of the sympathetic nervous 



C. THE VENTRAL SYMPATHETIC NERV- 

 OUS SYSTEM 



The ventral s\TTipathetic nervous 



system are given in dotted lines; system consists of a series of more or 

 ag, anterior ganghon; *g, posterior , . ., , , ^ j 



ganghon; /g, frontal ganghon; sn, less Similar elements, each connected 

 nerves of the salivary glands; r, ^ith a ganglion of the ventral chain 

 recurrent nerve (After Hofer). . , ° ^ • 



01 the central nervous system. 1 ypi- 



cally there is an element of this systein arising in each thoracic and 



