MORPHOLOGY OF ANIMALS 



Fig. 22. Nerve Cells and their Origins. A, Epithelial nervous system, the five large nerve 

 cells and the many nerve fibers (small circles) being part of the surface epithelium B ana 

 C, Epitheliogenous nervous systems. B, Delaminate Nervous System, the nerve cells and 

 fibers having split off from the surface epithelium ; C, Tubular Nervous System, the nerve 

 cells and fibers having folded in and then separated from the surface epithelium. D, Unipolar 

 Nerve Cell of an Annelid with one nerve fiber ( + ). E, Multipolar Nerve Cell of Electric Ray, 

 the fiber marked + is the neurite or axon, the others are dendrites. (After Hatschek). 



