Following on this picture he speaks of the way in which conscious actions become automatic and makes a statement to the effect that “_There is evidence to show that the axons_ (or processes of the nerve-cells which extend unbroken from nerve-cell to its termination) _become covered with a adulated coat as each new tract is formed. Thus the structure, like the habit, becomes fixed_”--and--“_It would appear as if, by repeated experiences, tracts and pathways must be beaten through the nervous system_”[83] (Italics not in original). [83] _Op. cit._, p. 371. Beside this I place a statement from Professor Graham Kerr as to his view of the development of peripheral nerve-trunks. He is reviewing the “outgrowth” theory of His, the “chain cell” theory of Balfour, and the “Primitive Continuity” theory of Hensen, and expresses himself as follows: “_It is suggested that the development of the actual nerve fibril is simply the coming into view of a pathway produced by the repeated passage of nerve impulses over a given route._”[84] (Italics not in original.) [84] _Text Book of Embryology._ Vertebrata with the exception of Mammalia. Vol. II., 1919, p. 106. A passage from Professor McDougall’s _Physiological Psychology_ may also be referred to at more length than it was in Chapter III., page 25. Speaking of the automatization of voluntarily acquired actions which have been explained by the view that purely reflex actions carried out by mechanisms of the spinal level were also originally acquired by our original ancestors as voluntary actions, he says, “This view is usually associated with the name of Wundt, who has forcibly advocated it. It implies, of course, the assumption that acquired characters are in some degree transmitted from one generation to another, a proposition which most biologists at the present time are inclined to deny because they cannot conceive how such transmissions can be effected. Nevertheless, the rejection of this view leaves us with insuperable difficulties when we attempt to account for the evolution of the nervous system, and there are no established facts with which it is incompatible. If, therefore, we accept this view we shall regard the congenital neural dispositions, both those that determine pure reflexes and those that determine instinctive actions, as having been acquired and consolidated under the guidance of individual experience, with the co-operation, to a degree which we cannot determine, of natural selection.”[85] [85] _Physiological Psychology._ W. McDougall, p. 156 (1911). These three statements from a physiologist, a zoologist, and a psychologist, all of great eminence, though they differ in particular problems studied, tell very strongly in favour of the position here put forward as to initiative in the production of specialised innervation of the skin. Origin of Cold, Warm, Pain and Touch Spots.