A CRAB 45 
mass, in the shape of a ring, which occupies a central position 
in the cephalothorax, and from which nerves radiate to the 
different appendages. The dorso-ventral artery passes through 
this rmg. Expose the entire nervous system. 
Exercise 6. Draw a semidiagrammatic view of the nervous 
system, being careful to represent accurately the nerves 
radiating from the ganglionic ring and those going from 
the brain to the eyes and to the antenne. 
