Nerve Cells 95 



servation and reproduction of invertebrates and 

 the three lowest classes of vertebrates ; it often 

 reaches so high a level that it is difficult to dis- 

 tinguish it from acts commonly attributable to 

 the work of intelligence. In the following 

 pages the origin and mode of action of a form 

 of nerve energy which is capable of infusing 

 intelligence into instinctive processes will be 

 explained. 



Nerve cells consist of a minute mass of 

 nucleated protoplasm. From the body- 

 substance of the cell fibres of two kinds extend 

 outwards; one set of these fibres soon after 

 emerging from the cell divides into several 

 branches, which either unite or come into rela- 

 tion with similar fibres from neighbouring cells ; 

 these fibres are called dendrites or dendrons. 

 Other fibrils passing from the nerve cell con- 

 stitute what is termed its axis cylinder; these 

 fibres often extend for a considerable distance 

 from the cell in which they take their origin, 

 and in their passage through the brain and 

 spinal cord give off branches to other cells, and 

 ultimately break up into a plexus of fibrils 

 which are distributed to muscle cells or other 



