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 by 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 sympathetic nerv^ous sys- 

 tem of insects ; nerves 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 oesophageal sympa- 

 thetic nervous system of Peri- 

 planeta orientalis; the outhnes of 

 the brain {b) and the roots of the 

 antennal nerve which cover a por- 

 tion of the sympathetic nervous 

 system are given in dotted lines; 

 ag, anterior ganglion; pg, posterior 

 ganghon; /g, frontal ganghon; sn, 

 nerves of the salivary glands; r, 

 recurrent nerve (After Hofer). 



THE VENTRAL SYMPATIlETIC NERV- 

 OUS SYSTEM 



The ventral sjonpathetic nervous 

 system consists of a series of more or 

 less similar elements, each connected 

 with a ganglion of the ventral chain 

 of the central nervous system. Typi- 

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



