3IO Journal of Comparative Neurology. 



sory series are both as it were ' functions ' of the anatomical 

 series. The motor series expresses the effects of the action of 

 all the anatomical mechanisms in the form of contraction of 

 muscles; the sensory series the effects of the same action of all 

 the mechanisms in the form of activity of the psychical appara- 

 tus. Only the direct (segmental) motor neurones have their 

 action expressed directly ; even the psychical apparatus mani- 

 fests its activity merely by the motor neurones (voluntary and 

 sympathetic), and all the mechanisms are known to us merely 

 by their effects on these. Parts of these results cannot be com- 

 pared directly with parts of the mechanism if we do not 

 care to stand in the way of our own progress as in the vexed 

 question of the localization of • sensations ' in the segments of 

 the neural stem. 



Retrospective Considerations. 



The neurone theory has for us the value of a working hy- 

 pothesis. It it closely connected with the cell-theory of tissues 

 generally. Many detail features, as the question of anasto- 

 moses, although they may be essential for the formulation of 

 certain versions of the neurone-theory, are still problematic. 

 The genetic side of the neurone-theory, the exclusive origin of 

 all the portions as parts of cells — is endorsed by almost every- 

 body ; the per.iisten:e of all these portions. — fibers, fibrils, etc. 

 — as parts of cells is also maintained by the great majority for 

 the nerve-elements but is abandoned by Weigert for the neu- 

 roglia. The importance of Nissl's, Bethe's, Apathy's and others' 

 objections is not sufficiently cleared yet. The independence of 

 the nerve-elements in the foetus and in the young is also gen- 

 erally admitted ; but the question of ultimate anastomoses in 

 adults is just now more unsettled than ever before. 



The laws of degeneration give a valuable line of support 

 to the cell-theory. The trophic influence of the cells on the 

 fibers is now reduced to the general laws of trophism of cells, 

 especially since we know that the relations of trophism between 

 fiber and cell are quite mutual, the cell-body being affected by 

 lesions of the fiber just as well as the fiber by a break of its 



