DR. HILL, PROM REFLEX ACTION TO VOLITION. 37 



How dull a paper this promises to be is the half-formed 

 thought of most minds in this room! But what a complex 

 product of experience is this simple thought : experience of 

 other papers, judgment of character, recollections of efforts 

 made to struggle with metaphysical subjects. 



The metaphysical side of the problem is the aspect which I 

 wish to avoid as far as possible. It is the thoughts of an anato- 

 mist that I have to offer. I must therefore ask you to follow 

 me in tracing the evolution of the nervous system from the 

 beginning. Which of all the mass of facts accumulated by 

 the patient research for the most part of very recent years 

 shall we select as steps on which to climb ? First we must 

 ask what is the ground from which we start — where in the 

 animal kingdom does the nervous system first appear ? 

 There are animals which have none; but it is not possible to 

 trace its genesis as clearly as we could wish. Some points, 

 however, are absolutely clear. It is certain, for instance, 

 that in ail animals the whole nervous system is formed from 

 the layer which, in the rest of its extent, becomes the skin. 

 It belongs to the surface of the body, the layer, that is to say, 

 which alone is exposed to the impact of impressions from the 

 outer world. It is also clear that before a nervous system is 

 formed, certain regions of the. surface are, owing to their 

 favourable situation, marked off as outposts for observation, 

 as sense-organs. From the epithelial cells of these sense- 

 organs, thin processes, or nerves, are prolonged to the muscle 

 fibres contraction of which enables the animal to make the 

 appropriate movement for escaping the danger, or seizing* 

 the food, of the presence of which the sense organ conveyed 

 information. It is also clear that the nervous system, properly 

 so called, is first formed by the deposition from the surface 

 of certain of these sensory cells, the union of whose processes 

 into a network or plexus, provides for the transmission 

 of the impulses received by their more fortunate sisters not 

 only to the muscle fibres, with which the cells on the surface 

 may be supposed to have been in primitive connection, but 

 also with a variety of muscles, the contraction of each of 

 which is appropriate to the particular hind of impression 

 received. Examine now the way in which this primitive 

 nervous system works. It may be said in the jelly-fish to 

 have reached the stage of evolution just described, and no 

 animal (as Dr. Romanes was the first to recognize) is more 

 accessible to experiment. It is not necessary for the purposes 

 of this paper to follow Dr. Romanes and others through the 



