No. 3] A STUDY IN FOOT STRUCTURE. 315 



especially in connection with the joints and in the fields of 

 variation and correlation. 



2. The determination of growth by pressure and strain is a 

 complicated matter. The palaeontological writers, however, I 

 understand to have advanced two propositions on the subject : 

 first, that the bones are governed in size by the mechanical 

 stimulus they receive ; second, that their conformation is deter- 

 mined in the same way, — regions of growth being determined 

 by regions of pressure and strain. Facts have been shown 

 inharmonious with both principles, while as to the second it 

 has been pointed out that the testimony of the literature is 

 conflicting. 



That lines of evolution have progressed with but few useless 

 side variations seems to be the uniform testimony of palaeontolo- 

 gists ; but that race changes follow those produced in the indi- 

 vidual life, or that they are directly caused by their mechanical 

 surroundings, I do not think has been satisfactorily shown. 



