THE REGULATING MECHANISM 181 



example, may extend unbroken to the foot. 

 It would appear they may divide and sub- 

 divide, and as the mass of matter must increase 

 as the fibre passes onwards, the material 

 forming the conducting central part of a 

 nerve-fibre must also increase. This has- 

 been well established in the electric fish 

 Malopterurus, In this animal the electric 

 organ in each half of the body is set into action 

 by the activity of one gigantic neurone in 

 each half of the spinal cord, each minute 

 portion of the electric organ is supplied by 

 a nerve fibre, and the sum of the diameters 

 of these fibres is many thousand times greater 

 than the diameter of the axon where it issues 

 from the giant neurone, 



100. The central nervous system is built up 

 largely of masses of neurones, supported by 

 neuroglia. These masses constitute what is 

 called the grey matter, found in the centre of 

 the spinal marrow and in and more especially 

 on the surface of the brain. Grey matter 

 is always supplied by a very rich plexus of 

 capillaries formed by the subdivision of arteri- 

 oles ramifying and subdividing in the mem- 



