NEOLAMARCKISM 



A^7 



In his essay "On Dynamic Influences in Evolu- 

 tion " W. H. Dall* holds the view that — 



" The environment stands in a relation to the in- 

 dividual such as the hammer and anvil bear to the 

 blacksmith's hot iron. The organism suffers during 

 its entire existence a continuous series of mechani- 

 cal impacts, none the less real because invisible, or 

 disguised by the fact that some of them are precipi- 

 tated by voluntary effort of the individual itself. 

 . . . It is probable that since the initiation of life 

 upon the planet no two organisms have ever been 

 subjected to exactly the same dynamic influences 

 during their development. . . . The reactions 

 of the organism against the physical forces and 

 mechanical properties of its environment are abun- 

 dantly sufficient, if we are granted a single organism, 

 with a tendency to grow, to begin with; time for 

 the operation of the forces; and the principle of the 

 survival of the fittest." 



In his paper on the hinge of Pelecypod molluscs 

 and its development, he has pointed out a number 

 of the particular ways in which the dynamics of the 

 environment may act on the characters of the hinge 

 and shell of bivalve molluscs. He has also shown 

 that the initiation and development of the columel- 

 lar plaits in Voluta, Mitra, and other gastropod mol- 

 luscs " are the necessary mechanical result of certain 

 comparatively simple physical conditions; and that 

 the variations and peculiarities connected with these 

 plaits perfectly harmonize with the results which fol- 

 low within organic material subjected to analogous 

 stresses. 



* Proceedings Biological Society of Washington, i8go. 

 27 



