LIGIA. 87 
Nervous SYSTEM. 
-The nervous system (PI. III., fig. 4) is composed of a 
series of paired ganglia, the ganglia of each pair being 
closely apposed; the ganglia are connected by distinct 
commissures. 
The supra-oesophageal or cerebral ganglion (cer. q.) 
extends across the space between the eyes, anterior and 
dorsal to the gut. The ganglion cells have large deeply- 
staining nuclei, and the fibres arising from them decussate 
and connect the gangla. In the supra-oesophageal 
ganglia several lobes can be distinguished. On the dorsal 
side there is a large pair of lobes, from the sides of which 
the optic stalks arise. Each of these optic stalks consists 
of a proximal lobe, connected by closely apposed parallel 
fibres with a distal lobe, from which the optic fibres arise 
and run direct to the retinulae. On the ventral sides of 
the superior lobes a small pair of median lobes is 
situated ; these are anterior to, and connected with, a larger 
pair of ventral lobes, the olfactory lobes, from which 
the large antennal nerves (ant.n.) arise. The supra- 
oesophageal ganglion is connected with the  sub- 
oesophageal ganglion by a pair of peri-oesophageal com- 
missures. 
The sub-oesophageal ganglionic mass is perforated 
near the anterior end by a vertical muscle band. The 
mouth-parts are innervated by two pairs of nerves (mm.p.n.), 
the first of which arises lateral to the perforation, and the 
second pair posterior to this, and latero-ventral. A pair 
of nerves (g.n.) arise posterior to these and run ventrally 
to the stomach. 
The sub-oesophageal ganglion is connected with the 
ganglia of the first thoracic segment by a pair of cords, 
from the middle of each of which a bifurcating nerve 
arises supplying the muscles of the body. 
