CHAPTER XI. THE OPINIONS OF 

 NEOLAMARCKIANS. 



T AMARCK ascribed some of the evolutionary changes 

 JL/ of structure to changes in the environment, some 

 to the motions of organic beings, and others to both 

 combined. 1 Spencer in 18652 devoted a short chapter 

 to the effect of motion in producing variations, and 

 specified the mechanical effect of flexure in producing 

 segmentation of the vertebral column. The present 

 writer in 1871 insisted on the importance of motion 

 as a factor in determining growth, and in 1872* I ap- 

 proached the subject more definitely in the following 

 language : " The first physical law is that growth force 

 . . . must develop extent in the direction of least re- 

 sistance, and density on the side of greatest resist- 

 ance." In 1877 Ryder further applied the principle 

 of motion to the origin of structural changes, chiefly 

 reduction of digits, in the feet of Mammalia in lan- 

 guage 5 which I have quoted on page 311. 



\Philosophie Zoologique, Chap. VII., 1809; translation in American Nat- 

 uralist for 1888. 



2 Principles of Biology ; II., pp. 167 and 195. 



^Proceeds. Amer. Philosoph. Soc., 1871, p. 259. Origin of the Fittest, 1887, p. 

 210. 



IPenn Monthly Magazine, July, 1872. Origin of the Fittest, 1887, p. 30. 



5 American Naturalist, 1877, p. 607. 



