Note 190 — Chapter VIII · THE LAWS OF NERVOUS ACTIVITY.

The mode of termination of nerves in muscles is still a point on which histologists disagree; probably because there is no abrupt termination, but a blending of the one tissue with the other. In the Tardigrades, for example, there is actually no appreciable distinction between nerve and muscle at the point of insertion of the nerve; and if in the higher animals there is an appreciable difference between nerve and muscle, there is an inseparable blending of undifferentiated substance at their point of junction. [According to Engelmann’s recent researches, there seems good reason to suppose that muscles are composed of contractile substance and a substance which is a modification of axis-cylinder substance; the first being doubly refracting, the second isotropic: Pflüger’s Archiv, 1875, p. 432.]