AND PHYSIOLOGY OF THE BRITISH ASSOCIATION. 713 



These hypotheses of Herbert Spencer, which have been widely 

 adopted in this country, are, it appears to me, not borne out by 

 the discoveries to which I have called your attention to-day. 

 The discovery that nerves have been developed from processes 

 of epithelial cells, gives a very different conception of their genesis 

 to that of Herbert Spencer, which makes them originate from 

 the passage of nervous impulses through a tract of mingled 

 colloids ; while the demonstration that ganglion-cells arose as 

 epithelial cells of special sense, which have travelled inwards 

 from the surface, admits still less of a reconciliation with Herbert 

 Spencer's view on the same subject. 



Although the present state of our knowledge on the genesis 

 of the nervous system is a great advance on that of a few years 

 ago, there is still much remaining to be done to make it com- 

 plete. 



The subject is well worth the attention of the morphologist, 

 the physiologist, or even of the psychologist, and we must not 

 remain satisfied by filling up the gaps in our knowledge by such 

 hypotheses as I have been compelled to frame. New methods 

 of research will probably be required to grapple with the pro- 

 blems that are still unsolved ; but when we look back and survey 

 what has been done in the past, there can be no reason for 

 mistrusting our advance in the future. 



B. 46 



