22 



THE USES AND ORIGIN 



be seen in its earliest form as a barely recognizable 

 structure in Sarsia.* 



From all this it would appear that the primitive ' nerve 

 fibre ' is a structure serving to connect impressions made 

 upon the exterior of the organism with certain responsive 

 muscular contractions quickly following thereupon. This 

 is perfectly true, though only part of the truth. 



The path taken by stimuli from impressible surfaces to 



muscles is not generally 

 the shortest and most 

 direct route. In the 

 great majority of organ- 

 isms these paths are 

 more or less bent upon 

 themselves. Those for 

 ingoing impressions may 

 run nearly parallel with 

 one another towards 

 some central situation ; 

 and thence they may be 

 distributed to muscles in 

 various parts of the 

 body — some of these 

 being perhaps not very 

 distant from the surface 

 stimulated. In the latter case the track of the stimulus 

 wave is found to be bent at an acute angle, or ' reflected.' 

 At the turning point or ' nerve centre,' whence impres- 

 sions are distributed outwards in various directions to 

 muscles, what are called ' Nerve Cells ' become developed. 



* Since the above was written and in type the observations of 

 Sohiifer (Proceed, of Koy. Soc, January, 1878), and of 0. and K. 

 Hertwif^, have revealed the existence of distinct nerve tissues in 

 several species of Medusae. 



FiG. 1.- Different kinds of Nerve Cells. (Magni 

 ficd about 850 diameters.) 



