MODERN EVOLUTION. 229 



which, in his pride of birth, man advances against 

 psychical continuity. Vain is the search after 

 boundary lines between reflex action and instinct, 

 and between instinct and reason. Barriers there are 

 between man and brute, for articulate speech and 

 the consequent power to transmit experiences has 

 set up these, and they remain impassable. " The 

 potentialities of language, as the vocal symbol of 

 thought, lay in the faculty of modulating and articu- 

 lating the voice. The potentialities of writing, as 

 the visual symbol of thought, lay in the hand that 

 could draw, and in the mimetic tendency which 

 we know was gratified by drawing as far back as 

 the days of Quaternary man " (Huxley's Essays on 

 Controverted Questions, p. 47). But these specially 

 human characteristics are no sufHcing warrant for 

 denying that the sensations, emotions, thoughts, and 

 volitions of man vary in kind from those of the 

 lower creation. " The essential resemblances in all 

 points of structure and function, so far as they can 

 be studied, between the nervous system of man and 

 that of the dog, leave no reasonable doubt that the 

 processes which go on in the one are just like those 

 which take place in the other. In the dog, there can 

 be no doubt that the nervous matter which lies 

 between the retina and the muscles undergoes a 

 series of changes, precisely analogous to those which, 

 in the man, give rise to sensation, a train of thought, 

 and volition." This passage occurs in Huxley's 

 Reply to Mr. Darwin's Critics, which appeared in 



