230 NERVE CELLS. 



and scarcely visible nerve fibres are however compound, 

 and consist of several very fine ramifications, each of which 

 may be capable of transmitting more than a single nerve 

 current. Such ultimate compound nerve fibres of mammalia 

 are so very transparent that they can only be seen in very 

 well prepared specimens. They have not, in fact, been 

 demonstrated by other observers, and some appear to 

 doubt whether they have been seen by me. In the white 

 mouse, rat, mole, and bat I have however observed the 

 appearances I have delineated in my drawings, in many 

 specimens, some of which have retained their characters for 

 upwards of ten years. Although the appearance represented 

 is to be seen clearly and definitely, the nerve structure is so 

 very delicate and transparent that it can only be studied 

 under high powers, with the aid of carefully focussed illu- 

 mination. Fine peripheral nerve fibres in the frog, in which 

 animal they may be demonstrated much more easily than in 

 mammalian animals, are also represented in Pis. XIII, 

 XIV, and XV. 



Nerve Cells. A simple form of peripheral nerve ele- 

 mentary part or cell is represented in fig. i, PI. IX, and in 

 many nerve centres there are cells of a structure and 

 arrangement as simple. All central, like all peripheral, nerve 

 cells, have at least two fibres proceeding from them, and 

 these, 'either at once or at a short distance from the cell, 

 pursue opposite directions. In many cases the nerve cell 

 belonging to a nerve centre exhibits several fibres which 

 pursue different courses, sometimes appearing to radiate 

 from the cell as from a centre. The constituent ramifica- 

 tions of the fibres, however, traverse the body of the cell, and 

 pursue a continuous course through its substance. The 



