ARCHITECTURAL CHANGES DUE TO GROWTH. 23! 



On examining the developing system, the neuroblasts 

 are found to be spherical and possessed of one process 

 only, the neuron. It would be hasty to infer that 

 elements in this stage of development were unorganised, 

 since a central system apparently in this condition can 

 give complex reactions. 1 In seeking an explanation 

 for such a case, it should be remembered that if the 

 impulses pass between fully-developed nerve elements 

 by means of their contiguous outgrowths, then in the 

 earlier stages of growth the contiguity of cell-bodies 

 themselves might furnish a sufficient though less delicate 

 arrangement for their transmission. In the mature 

 system, however, organisation depends on development 

 of the cell outgrowths. The most important of these, 

 the neuron, is the first to appear ; later, the dendrons. 

 By means of the former, distant connections are estab- 

 lished if it so happens that the neuron pursues a long 

 course as a main stem, having but a few lateral branches 

 near its origin. If, on the other hand, the neuron at 

 once breaks up into many branches in the neighbour- 

 hood of the cell-body, these, like the lateral branches of 

 the main stem, are looked upon as the basis of local 

 connections. 



Not only ontogenetically, but phylogenetically also, 

 the dendrons appear latest. They must, therefore, be 

 considered as important to the better organisation of 

 the central system. That changes in the size and 

 form of the elements usually accompany organisation is 

 amply evident, though these changes are not necessarily 

 correlated, for a system composed of small cells may 

 yet be well organised. 



It has been so long customary to describe the nerve 

 cells without much analysis of them, that a number of 

 peculiarities in the individual elements have but recently 

 1 His, Kef), lot A Intemat. Afed. Co:ig.< 1890. 



