THE SYMPATHETIC SYSTEM 



239 



nerve (nr, vagus of Newport). The first of these ganglia is the 

 frontal ganglion, which is connected with the oesophageal ganglia by 

 a pair of roots (rvt), which have an origin primitively common with 

 that of the labral nerves (Fig. 248, fg and Ibr). 



2. Of two pairs of lateral ganglia (Fig. 255, ga, gp) situated two on 

 each side of the oesophagus. They are connected both with the 

 antennal lobes by a nerve (rvd), and to the chain of unpaired ganglia 

 by a special connective. The first 

 pair of these ganglia sends nerves 

 to the heart and aorta ; the second 

 pair to the tracheae of the head. 



The unpaired median or recur- 

 rent nerve (nr) extends back from 

 under the brain along the upper 

 side of the oesophagus, and (in 

 Blatta), behind the origin of the 

 nerves to the salivary glands, 

 enters an unpaired ganglion, called 

 the stomachic ganglion (ganglion 

 ventriculare), situated in front of 

 the proventriculus. The number 

 of these stomachic ganglia varies 

 in different orders of insects. 



In Blatta, Kiipffer and also Hofer l-iv5<l 



have shown (Fig. 255) (Miiller, Brandt, 

 ex Kolbe) that the nerve to each sali- 

 vary gland arises from three different 

 centres : the anterior end situated under 

 the oesophagus is innervated by the 

 paired visceral nerves from the hinder 

 paired ganglia ; the remaining part by 

 nerves arising from each side of the 

 recurrent nerve ; and thirdly by a pair 

 of nerves arising from the subcesophageal 

 ganglion which accompanies the com- 

 mon salivary duct, and ends in branches which partly innervate the salivary 

 glands and in part their muscles. 



Hofer considers that the function of this complex system of paired 

 and unpaired ganglia, with their nerves, is a double one, viz. serving 

 both as a centre for the peristaltic action of the oesophagus, and as 

 innervating the salivary glands. 



Besides these a second portion of the visceral system arises from 

 the thoracic and abdominal ventral cord. It may be seen in the 



FIG. 255. Anterior portion of the paired 

 and unpaired visceral nervous system of Blatta 

 orientally seen from above. The outlines of 

 the brain ((/) and the roots of the antennal nerve 

 (), which cover a portion of the sympathetic 

 nervous system, are given by dotted lines. 

 Lettering as in Fig. 247. nxd, nerve to salivary 

 gland. The nervus recurrens (nr) enters an 

 unpaired stomach ganglion farther back. Af- 

 ter Hofer, from Lang. 



