CHAPTER XL THE OPINIONS OF 

 NEOLAMARCKIANS. 



T AMARCK 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. 1 Spencer in i865 2 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 iSyi 3 insisted on the importance of motion 

 as a factor in determining growth, and in i8j2 4 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. 

 2io. 



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

 5 American Naturalist, 1877, p. 607. 



