NO. 4 



NERVOUS SYSTEM OF A CENTIPEDE — LORENZO 



17 



posterior ganglion is more ventrally situated than the anterior one. 

 The esophagus passes between them and is bounded laterally by the 

 circumesophageal connectives, which run in an anterodorsal-postero- 

 ventral direction (fig. 3). 



Viewed from the dorsal aspect the supraesophageal ganglion is rela- 

 tively simple and almost circular. Transversely it is slightly wider 



Fig. 3. — Arenophilus bipuncticeps (Wood), sagittal view of the head, showing 

 the cephalic neural mass in relation to the exoskeletal structures and the 

 esophagus (OES). The position of the two pairs of giant cells located in the 

 subesophageal ganglion (SBG) is indicated by x's. 



than it is long by a ratio of 9:7. The lateral and posterior borders 

 are rounded in a smooth arc. The antennal nerves emerge anteriorly 

 and are more widely separated than the posterior circumesophageal 

 connectives. In the median plane a depression is seen anterior to the 

 crossed dorsal tracheae (fig. i). This is the exit of a canalicular 

 structure, the "cerebral artery," which courses in an oblique postero- 

 ventral direction (see fig. 5, B, and pis. 3 and 4). 



The most striking feature on the ventral surface of the supra- 

 esophageal ganglion is a pair of circumesophageal connectives. These 

 are continuous with the tritocerebrum which is poorly developed (fig. 

 2). The cerebral gland is laterally situated and projects beyond the 

 lateral margin of the frontal lobe. A small nerve (N4) innervates 

 this gland (fig. 2). A larger nerve (Ne) emerges from the frontal 

 lobe adjacent to the cranial border of the gland. The median recurrent 

 nerve (N14) emerges between the tritocerebral lobes and is closely 

 associated with several other small nerves. These are described in the 

 following section. 



The subesophageal ganglion is an elongate mass located ventral to 



