SEA-FISHERIES LABORATORY. 211 



ganglia are connected by broad commissures passing on 

 each side of the oesophagus, leaving only a narrow opening 

 for its passage. The sub-cesophageal ganglion projects 

 slightly forward under the supra-oesophageal, 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-cesophageal ganglion is about half the size 

 of the sub-oesophageal. 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). Each 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 setae 

 clothing the anterior surface of the basal joint and apex 

 oi the second (Plate III., fig. 4). From the manner in 

 which the antennules are supplied by this nerve it is 

 evident that they are important sensory organs (Plate III., 

 fig 4). 



The antennae 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 antennae. These are the only appendages supplied 

 from the supra-cesophageal ganglion. 



The sub-cesophageal ganglion is heart-shaped, and fully 

 twice the size of the supra-oesophageal. It represents the 

 whole of the thoracic and abdominal ganglia of the higher 

 Crustacea, and supplies the remainder of the appendages. 



