CHAPTER XI.— THE OPINIONS OF 

 NEOLAMARCKIANS. 



1AM ARCK ascribed some of the evolutionary changes 

 J of structure to changes in the environment, some 

 to the motions of organic beings, and others to both 

 combined.^ Spencer in 1865^ 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^ which I have quoted on page 311. 



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

 uralist for 1888. 



^Principles of Biology, II., pp. 167 and 195. 



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



210. 



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

 h American Naturalist, 1877, p. 607. 



