New Muscles.

If it can be said without fear of question that “the differentia­tion of muscle and nerve is the morphological result of division of labour, whereby the unit of protoplasm, in which irritability and contractility are combined, has, on the one hand, become modified into muscle, which retains the property of contractility, and on the other into nerve, which retains that of irritability,”[73] and if Wolff’s Law of Bone Transforma­tion teaches that if a normal bone is used in a new way its structure and form will change to meet its new function, which Sir Charles Bell had more vaguely taught in 1834, it cannot well be denied that at certain turning-points in the history of animal organisms the sequence of changes which arise is neural change, muscular modifica­tion and finally change of bone, whether ungulates, carnivores, felidæ, gibbons or big anthropoids or man, be the dramatis personæ. The only question is whether selection or use and habit initiates the subtle and slow process.