72 .CHAPTERS ON EVOLUTION. 



cesses of its substance along the communicating channels already 

 alluded to, and thus communicates with the living matter of the 

 neighbouring spaces. So that, could we obtain a perfect view of the 

 living protoplasm of a bone, we should find f.hat, when removed from 

 the lacunae, these living parts would appear before us somewhat like 

 a spider's web, and as a connected series of Amceba-like masses of 

 protoplasm, adhering together by the minute processes just described, 

 and roughly reproducing for us the form and outline of the bone. 

 These masses of protoplasm are the " cells " of the bone on which 

 depend the life, nourishment, and general welfare of that structure. 

 We thus learn the curious fact that the most solid and enduring tissue 

 of our body, in its essential nature, represents a collection of Amceba- 

 like masses of protoplasm absolutely undistinguishable, be it also 

 remarked, in nature from the similar matter which moves and gropes 

 in the gutters of our housetops or in the stagnant pools. As the 

 plant-cell imprisons its protoplasm within a thick cell-wall, so our 

 bone-cells in like manner form our skeleton by their special manner 

 of growth and development And it requires no great depth of 

 thought to perceive the similarity of the elements of the human tissue 

 to those which constitute the essentials of lower life at large. 



Not less striking are the revelations which research into the funda- 

 mental structure of the nervous system displays. Nerve-cells (Fig. 22, 

 t,d)a.nd nerve-fibres together comprise the body's telegraph system; the 

 fibres of nerves being primitively formed like other fibres of the body 

 from cells. The nerve-cell has come to be fully recognised as that part 

 of the nervous mechanism which produces and evolves nerve-force 

 that subtlest of life's forces, now seen to be represented in the 

 movement of a limb, and now in the impassioned utterances of mind. 

 The nerve-fibre simply carries and distributes the nerve-force gene- 

 rated by the cells, but possesses on its own account no power of 

 evolving the characteristic force that in varied fashions rules the 

 wide universe of human life and of lower existence as well. When 

 the structure of the brain and spinal cord, as the two chief nerve- 

 centres of the body, is examined, both cells and fibres are found to 

 enter into their composition; but the cells alone exist in those parts 

 such as the grey or external layer of the brain in which nerve-force 

 is evolved. Nerve-cells vary in size and shape. They may be 

 simple (Fig. 22, d) or complex (c] in form, and range from the round 

 or spherical to the branched and irregular in form. Some of the 

 " multipolar " (c) nerve-cells as those possessing a plurality of pro- 

 cesses are named might well enough suggest to the imaginative mind 

 a resemblance to Amoeba in shape, as they of a certainty are related 

 to that animalcule in the protoplasmic nature of their contents and 

 structure. For the essential element in the nerve-cell is protoplasm, 

 pure and simple ; undistinguishable in its chemistry and histology 



