INTRODUCTION. 15 



C. B. Wilson in his work on "North American Parasitic 

 Copepods belonging to the Family Caligidae," Part 1.* 



NERVOUS SYSTEM. 



The nervous system of C aligns and Lepeophtheirus, 

 and probably also of the other members of the Cali- 

 goida, appears to be very similar. It is composed of 

 two central ganglia and the paired nerves which arise 

 from them. One ganglion, the supra-cesophageal, lies 

 above the oesophagus, and the other, the sub-oesopha- 

 geal, immediately below it. The ganglia are practi- 

 cally fused together by the wide commissures which 

 join them. A very narrow opening is left in the 

 centre for the passage of the oesophagus. These are 

 the only ganglia, and they supply the various parts 

 of the body with nerves. The supra-oesophageal 

 ganglion is about half the size of the sub-oesophageal. 

 It is produced on its dorsal surface into an optic lobe 

 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, and each optic 

 nerve, therefore, is supplied by fibres from both sides 

 of the brain. The only other nerves that have their 

 origin in the supra-oesophageal ganglion are those 

 which supply the antennules and the antennse. The 

 nerves of the antennules divide into a number of 

 branches after they enter these appendages, and every 

 seta on the surface of the basal joint and apex of the 

 second branch is supplied with fibres. It is evident 

 that they are important sensory organs. The sub- 

 oesophageal ganglion is heart -shaped, and fully twice 

 the size of the supra-oesophageal. It supplies the 

 nerves to the remainder of the appendages. The 



* ' Proc. U. S. National Museum/ vol. xxviii, 1905. 



