life: its nature, origin, and maintenance SCHAFEE. 515 



hand, they continued to transmit these impressions to other, more 

 distant cells by their efferent prolongations. In the further course 

 of evolution the nei-vous system thus laid dowTi became differentiated 

 into distinct afferent, efferent, and intermediary portions. Once 

 established, such a nervous system, however simple, must dominate 

 the organism, since it would furnish a mechanism whereby the indi- 

 vidual cells would work together more effectually for the mutual 

 benefit of the whole. 



It is the development of the nervous system, although not pro- 

 ceeding in all classes along exactly the same line, which is the most 

 prominent feature of the evolution of the Metazoa. By and through 

 it all impressions reaching the organism from the outside are trans- 

 lated into contraction or some other form of cell activity. Its for- 

 mation has been the means of causing the complete divergence of the 

 world of animals from the world of plants, none of which possess any 

 trace of a nervous system. Plants react, it is true, to external 

 impressions, and these impressions produce profound changes and 

 even comparatively rapid and energetic movements in parts distant 

 from the point of application of the stimulus — as in the well-known 

 instance of the sensitive plant. But the impressions are in all cases ' 

 propagated directly from cell to cell — not through the agency of 

 nerve fibers; and in the absence of anything corresponding to a 

 nervous system it is not possible to suppose that any plant can ever 

 acquire the least glimmer of intelligence. In animals, on the other 

 hand, from a slight original modification of certain cells has directly 

 proceeded in the course of evolution the elaborate structure of the 

 nervous sj^stem with all its varied and complex functions, which 

 reach their culmination in the workings of the human intellect. 

 "What a piece of work is a man! How noble in reason! How 

 infhiite in faculty! In form and moving how express and admirable! 

 In action how like an angel! In apprehension how like a god !" But 

 lest he be elated with his psychical achievements, let him remember 

 that they are but the result of the acquisitiori by a few cells in a 

 remote ancestor of a slightly greater tendency to react to an external 

 stimulus, so that these cells were brought into closer touch with the 

 outer world; while on the other hand, by extending beyond the cir- 

 cumscribed area to which their neighbors remained restricted, they 

 graduall}' acquired a dominating influence over the rest. These 

 dommating cells became nerve cells; and now not only furnish the 

 means for transmission of impressions from one part of the organism 

 to another, but in the progress of time have become the seat of 

 perception and conscious sensation, of the formation and association 

 of ideas, of memory, of volition, and all the manifestations of the 

 mind. 



