CHAPTER III. 



THE FUNDAMENTAL PROPERTIES OF NERVOUS 

 TISSUES. 



IN its simplest, and probably earliest form, a nerve is nothing more 

 than a thin strand of irritable protoplasm, forming the means of 



FIG. 16. DIAGRAM TO ILLUSTRATE THE SIMPLEST FORMS OP A NERVOUS SYSTEM. 



A. An ectoderm cell e.c., with its muscular process m.p., as in Hydra. 



B. The ectoderm cell e.c. is connected with the muscle cell m.c. by means of the 

 primary motor nerve m.n. 



C. The differentiated sensitive cell s.c. is connected by means of the sensory 

 nerve s.n. with the central cell c.c. , which is again connected by means of 

 the motor nerve m.n. with the muscle cell m.c. 



