REGISTERING GANGLION. 271 



It is this sameness of action to which we allude in that popular expres- 

 sion, common sense a term full of meaning. In the origination of a 

 thought there are two distinct conditions involved the state of the mind 

 as dependent on antecedent impressions, and the existing physical cir- 

 cumstances. The brain is the instrument on which external circum- 

 stances play ; but in the same manner that the course of time presents 

 us with natural vicissitudes, such as night and day, the seasons, the tides, 

 spring and neap, with their ebb and flow, variations of events may ensue, 

 notwithstanding the fate-like aspect of the acting law, and this through 

 the interaction of consequences. So the earth revolves round the sun 

 as a consequence of gravity, and for the same reason does the moon re- 

 volve round the earth ; for the same cause do the tides flow and ebb in 

 the sea ; yet there will be spring tides when the sun and moon draw in 

 one direction, and neap tides when they draw in opposite ways. Out of 

 the invariable the variable may therefore arise. 



To return from this digression to the phenomena displayed by regis- 

 tering ganglia, in continuation of the views offered, I may pre- Illustration of 

 sent as an example the manner in which I should be disposed ^ 8 yjj in 

 to regard in this respect the entire nervous system of the ar- sects. 

 ticulata. Constructed as these animals are upon an axis, the nerves 

 which are given off from the ganglia upon that axis right and left, a pair 

 for each segment, are primarily purely automatic, and act therefore pri- 

 marily in a purely reflex way ; an impression made on the peripheral ex- 

 tremity of one of their centripetal fibres is conducted to the ganglion, 

 passes through it, escapes along the centrifugal fibre, and a motion oc- 

 curs. But the whole influence is not thus promptly disposed of. A part 

 of it is conducted by commissural strands to the cephalic ganglia, and 

 there held in reserve. And the same thing holds good for ev- Function of 

 ery one of the ganglia of the ventral cord, so that for them all the cephalic 

 the cephalic become a point of common convergence, or, in my gang ia ' 

 view, the common register for them all. Here, at this focal point, are 

 stored up the relics of whatever impressions have been made upon the 

 common peripheral nerves, and here are received those which are brought 

 from the structures of special sense the visual, the auditory, the olfac- 

 tory, if any. There does not, then, appear any great difficulty in ex- 

 plaining the well-marked deviations from automatism which these ani- 

 mals may present. 



The action of every ganglionic mechanism depends upon the existence 

 of certain physical conditions, among which, as being of par- Nerve centres 



-, -, . ^ T , . , i -J can not act ex- 



amount importance, one may be discerned. It is the due cept by ox j ( i a . 

 supply of arterialized blood. If this be stopped but for a tion - 

 moment, the nerve mechanism loses its power, or if diminished, the dis- 

 play of its characteristic phenomena correspondingly declines. If, on 



