468 



COMPARATIVE ANATOMY 



CHAP. 



centrated in the imago. Myrmeleon is, however, a case of adaptation of the nervous 

 system to the short compressed form of body of the larva. 



net JTT d <rf 



i i *J 



710 



ff* 



f&r 



FIG. 326. Median longitudinal section through the head of Blatta orientals. The nervous 

 system of the head is drawn entire, hyp, Hypopharynx ; os, oral cavity ; Ibr, upper lip ; gf, ganglion 



frontale ; g, brain ; na, root of the antennal nerve ; 

 TIO, root of the optic nerve ; ga, anterior ; gp, pos- 

 terior ganglion of the paired visceral nervous system ; 

 oe, oesophagus ; c, cesophageal commissure ; usg, 

 infra-oesophageal ganglion ; cc, longitudinal commis- 

 sure between this and the first thoracic ganglion ; 

 sg, common duct of the salivary glands ; Ib, lower 

 lip = 2d pair of maxillae ; nr, nervus recurrens ; d, 

 nerve uniting the frontal ganglion with the oeso- 

 phageal commissure ; e, nerve from this commissure 

 to the upper lip ; /, nerve from the infra-oesophageal 

 ganglion to the mandible ; g, to the anterior max- 

 illae ; h, to the lower lip (after Bruno Hofer). 



(5) In many cases where in the larva 

 there is an apparently concentrated ventral 

 chord, its ganglia are quite distinct although 

 lying very close together. In the imago 

 they separate and the longitudinal commis- 

 sures become distinct, so that a non- con- 

 centrated or less concentrated imaginal 

 nervous system is developed. 



The sympathetic nervous system seems 

 to be present in all Antennata. It consists 

 of an unpaired and a paired system. In 

 Blatta, whose visceral nervous system (Figs. 

 326 and 327) has been the most investigated, 

 the unpaired portion shows the following 

 arrangement. In front of the brain on the 

 oesophagus there lies an unpaired ganglion 

 frontale gf, which gives off nerves to the 

 upper lip and the oesophagus. It is con- 

 nected by a nerve on each side with the 

 cesophageal commissure, from which another 

 nerve as well goes off to the oesophagus and 



FIG. 327. Anterior portion of the paired 

 and unpaired visceral nervous system of 

 Blatta orientalis, seen from above. The 

 outlines of the brain (g) and the roots of the 

 antennal nerve (na), which cover a portion of 

 the sympathetic nervous system, are given by 

 dotted lines. Lettering as in Fig. 326. nsd, 

 Nerve to salivary -gland. The nervus recurrens 

 (nr) enters an unpaired stomach ganglion 

 further back (after Bruno Hofer). 



