-JO BRISTOL. 



DESCRIPTION OF PLATE VII. 



Fig. i6. Lateral view of the nervous system of the head region, reconstructed 

 from sections, showing the distribution and general paths of the principal nerve 

 trunks, the intermuscular nerve rings in annul! 5, 8, and 11, together with their 

 junctions with the central system, and other details. The principal eyes lie in 

 annulus 2, the small ventral branch of nerve II passing through it axially to the 

 labial sense organs. The second and third eyes look to the rear. On nerves I, 

 II, III, and IV the " Leydig's cells " of those neuromeres lie outside of the nerve 

 trunks which are the fused anterior and posterior lateral nerves of their respective 

 neuromeres. In nerves V and VI the same cell is seen near the angle of separa- 

 tion of the fused parts. 



Fig. 17. A reconstruction showing the general arrangement of the sympathetic 

 system. Combined from sections and specimens killed in Haller's fluid. The 

 body outUne is drawn from a median section, the same as used in Fig. 16, and 

 the parts of the central nervous system are traced in outline from Fig. 16. The 

 right half of the oesophagus is shown covered with the closed meshes of the 

 plexuses formed by the fibers from the multipolar cells. The cells are inadequately 

 shown ; see Fig. 20, PI. VIII. Standing out from the median side of each half 

 collar, median to the fused roots of nerves I, II, is a fibrous projection which 

 gives rise to three trunks: (i) one going ventral and median, meeting the similar 

 trunk of the other side in the mid-ventral line ; they form anastamoses and 

 gradually lose their outlines in the general plexus ; (2) a lateral trunk that persists 

 to the rear as shown ; (3) a dorsal branch which runs parallel with the collar to 

 the median dorsal line ; the details of this arrangement are shown in Fig. 20. 

 The dorsal trunk of each side carries two small capsules containing nerve cells, 

 while a third capsule, whose fibers go into the sympathetic system, is located on 

 the collar, not far from the origin of the connection between the central system 

 and the sympathetic. Anterior to the collar the sympathetic system runs to the 

 buccal cavity in fibrous bundles, apparently free from cell bodies. 



