1894.] The Energy of Evolution. 215 
The effect of motion or use on the soma may be conven- 
iently termed autokinetogenesis. Moderate use of a muscle is 
known to increase its size. Irritation of the periosteum is known 
to cause deposit of bone. - Friction and pressure of the epithelium 
increases its quantity or changes its form. Increased activity 
of the functions of nervous tissues increases their relative pro- 
portions, as in the enlargement of nerves which replace others 
which are interrupted by mutilations, etc. On the other 
hand, it is equally well known that disuse produces diminution 
of muscular tissue, and through it, a reduction in the quantity 
of the harder tissue (bone, chitin, etc.) to which it is attached, 
(as muscular insertions, etc.). It was the observation of such 
well-known phenomena as these that led Lamarck to advance 
his doctrine of evolution under use and disuse, and which has 
led many others to give their adherence to such a view. 
Thus much for cell-growth. Another class of modifications 
of a similar kind may be found in the parts of an organism 
which consist of a complex of cells, or tissues. Thus the lumen 
of a small artery is enlarged under the influence of pressure 
when it is compelled to assume the function of a larger vessel 
through the interruption of the latter. A part of an internal 
or external skeleton which is fractured will form an artificial 
joint at the point of fracture, if the adjacent surfaces are kept 
in motion. Marey (Animal Mechanism pp. 88-89) says “ After 
dislocations the old articular cavities will be filled up and dis- 
appear, while at the new point where the head of the bone is 
actually placed, a fresh articulation is formed, to which noth- 
ing will be wanting in the course of a few months, neither 
articular cartilages, synovial fluid, nor the ligaments to retain 
the bone in place.” I have given some illustrations of this fact,’ 
which have come under my observation, and which have an 
important bearing on the origin of the articulations of the 
vertebrate skeleton as I have traced them throughout geolog- 
ical time. I have as I think conclusively shown that these 
varied structures have been produced by impacts and strains, 
which are concomitants of the movements of the animals, act- 
ing through long periods of time” I have also proposed the 
Proceeds. Amer. Philos. Soc. 1892, p. 285. 
Te age Origin of the Hard parts of the Mammalia, Amer. Journal of Morpho- 
Origin of the Fittest, 1887, pp. 305-373. 
