56 
ganglia are connected by broad commissures passing on 
each side of the esophagus, leaving only a narrow opening 
for its passage. The sub-cesophageal ganglion projects 
slightly forward under the supra-csophageal, giving it 
the appearance of being separated from it, when viewed 
from the ventral aspect (Plate III., fig. 2). These are 
the only ganglia, and they supply the various parts of the 
body with nerves. 
The supra-csophageal ganglion is about half the size 
of the sub-cesophageal. It is produced on its dorsal 
surface into an optic lobe (Plate III., fig. 5), from which 
arises a distinct pair of optic nerves. Horizontal sections 
of the optic lobe show that the roots of these nerves cross 
each other (Plate III., fig. 12). Hach optic nerve, there- 
fore, is supplied by fibres from both sides of the brain. 
The nerves supplying the antennules arise from near 
the anterior angles of the ganglion. They pass obliquely 
forward to the base of the antennules, and there sub- 
divide into a number of branches which pass to the sete 
clothing the anterior surface of the basal joint and apex 
oi the second (Plate IIL, fig. 4). From the manner in 
which the antennules are supplied by this nerve it 1s 
evident that they are important sensory organs (Plate IIL., 
fig 4). 
The antenne are supplied by nerves arising from the 
anterior angles of the ganglion, which pass anteriorly 
under the nerves of the antennules and enter the base 
of the antenne. These are the only appendages suppled 
from the supra-cesophageal ganglion. 
The sub-cesophageal ganglion is heart-shaped, and fully 
twice the size of the supra-cesophageal. It represents the 
whole of the thoracic and abdominal ganglia of the higher 
crustacea, and supplies the remainder of the appendages. 
