70 INSTINCT, REASON, ETC. 



tion of differences in degree, acting through natural selection 

 in tlie vast eras of time that Science proves to have elapsed 

 since the earth was fit for the reception of life ; and that just 

 as in the physical so in the psychical realm in the struggle for 

 existence any slight variation from the parent forms that 

 gave its possessor an advantage over its fellows, and would 

 tend, from the same cause, by re-action, to go on developing 

 would leave its impress on the progeny ; and by correlation of 

 growth taking place in other organs, in time a totally different 

 looking creature would be evolved. Bear in mind, however, 

 that a great controlling force would be exerted by that 

 powerful factor in evolution, " tendency to revert to a former 

 type." 



The influence of environment also must not be forgotten 

 as one of the factors at work to produce modifications of 

 structure and function. 



Thus, just as it has been ascertained, that the differences 

 between a nebula, a sun and a planet ; between ice, steam, 

 and water ; between the hoof of a horse and the paw of a cat ; 

 between the fishes' air-bladder and gills, and a man's lungs, 

 are merely differences in degree produced by natural selec- 

 tion ; so surely are the simple reflex actions performed by the 

 jelly-fish, the instructive actions performed by the bird, and 

 highly rational and complex acts and thoughts emanating 

 from a Shakespeare, a Sir Frederick Leighton, or a Herbert 

 Spencer, merely accumulated differences in degree resulting 

 in a vast difference in kind. 



Just here let us take a brief glance at our diagram, and 

 notice where the seats of the various psychical acts lie in the 

 nervous system of a human being ; and as we dwell on the 

 differences in their anatomical features, I will endeavour to 

 give concise definitions of the functions they perform as 

 expounded by modern scientists. 



Professor Romanes' definitions are, I think, accepted in 

 the main as most nearly exact ; but while I accept his defini- 

 tions, I cannot help thinking in spite of Romanes' disagree- 

 ment that the famous hypothesis of Descartes' " Animal 

 Automatism," now rather tabooed by men of Science, will 

 account for many acts now classed as conscious or instructive. 



I now will quote Professor Romanes' own words. " Reflex 

 Action is non-mental neuro-muscular adjustment, due to the 

 inherited mechanism of the nervous system, which is formed 

 to respond to particular and often-recurring stimuli, by giving 

 rise to particular movements of an adaptive though not of an 

 intentional kind." 



