ON NEUROGENESIS 341 



tion in the substance of the neuroglial areas, where it 

 becomes available for absorption by the nerve cell den- 

 drons, for plastic arrangement by the cell and its nucleus 

 and nucleolus, for circulatory disposal by the axonal 

 processes to the related skin, and muscle, structures, by 

 direct continuity of histological circulatory channels, and 

 for subsequent structural incorporation with the textural 

 elements of the skin, and the sarcous elements of the 

 muscle fibres, through the sensory, and motor, fibres, 

 respectively. Each neuronal unit, as thus produced, and 

 nourished, becomes subservient to sensory, motor, or 

 psychic, purposes, according to its histological position, and 

 relationships, and remains devoted to its originally assigned 

 work, so that no one unit can take the place of another, 

 nor the gap be filled up when one is removed. 



Sleep affords a diurnal opportunity for the renewal and 

 redistribution of neuronal substance, and nerve energy, by 

 sympathetic nerve agency, and thus becomes the means of 

 the proper " linking up," and reciprocal, or co-ordinate, 

 working of the combined systemic, and sympathetic, nervous 

 systems. 



The evolution of the systemic nervature from the neural 

 division of the neurenteric canal resembles closely the 

 evolution of the alimentary, and associated, organisms, from 

 the enteric division of that canal, these two great develop- 

 mental processes jointly securing the innervation, and 

 nutrition, and, therefore, the life of the entire organism, 

 material, and dynamical. In effecting these results we 

 must recognise the principle of circulation as the chief 

 instrument, the operation of which along definite lines of 

 vasculature, and inter-space areas, effects the arrangement of 

 the formative elements into textures and organs, suitable 

 for carrying out the organic and functional work of the 

 living body, by a process of continual transference, whereby 

 the new elements of food and drink assume the structural 

 form of every tissue, and finally represent the residual or 

 complete result of all intra-corporeal vital change, and 

 activity. 



