THE NERVOUS SYSTEM 173 



Vertebrate Nervous System. — The central nervous system of 

 vertebrates, consisting of the brain and spinal cord, is a hollow 



1 i t 



Fig. 113. — Portion of ventral cord of the earthworm with two ganglia and six 

 pairs of lateral nerves. The sensory nerves end in terminal branches which con- 

 nect with the dendrites of the motor and coordinating nerve cells of the cord. 

 {From Calkins, Biology, Henry Holt & Company, Inc., after Retzius. By permission.) 



structure that develops from an embryonic neural tube. The 

 embryonic primordium of the vertebrate nervous system consists 



