THE INNER TISSUES OF ANIMALS. 351 



that the slowness of the ultimate ossification of this part, is 

 due to its non-vascularity, and to mechanical conditions 

 which are unfavourable to its acquirement of vascularity. 

 Once more, there is the demurrer that in the epiphyses ossifi- 

 cation does not begin at the surface but within the mass of 

 the cartilage. Explanation of this implies ability to follow 

 out the mechanical actions in a resilient substance which, like 

 india-rubber, admits of being distorted in all ways by pressure 

 and recovering its form, and it seems impossible to say how 

 the more superficial and more deep-seated canals traversing 

 it will be respectively affected. 



Of course it is not meant that this osseous development 

 by direct equilibration takes place in the individual. Though 

 it is a corollary from the argument that in each individual 

 the process must be furthered and modified by the particular 

 actions to which the particular bones are exposed; yet the 

 leading traits of structure assumed by the bones are assumed 

 in conformity with the inherited type. This, however, is no 

 difficulty. The type itself is to be regarded as the accumu- 

 lated result of such modifications, transmitted and increased 

 from generation to generation. The actions above described 

 as taking place in the bone of an individual, must be under- 

 stood as producing their total effect little by little in the 

 corresponding bones of a long series of individuals. Even if 

 but a small modification can be so wrought in the individual, 

 yet if such modification, or a part of it, is inheritable, we 

 may readily understand how, in the course of geologic epochs, 

 the observed structures may arise in the assigned way. 



Here may fitly be added a strong confirmation. If we find 

 cases where individual bones, subject in exceptional degrees 

 to the actions described, present in exceptional amounts the 

 modifications attributed to them, we are greatly helped in 

 understanding how there may be produced in the race that 

 aggregate of modifications which the hypothesis implies. 

 Such cases occur in ricketty children. I am indebted to Mr. 

 Busk for pointing out these abnormal formations of dense 

 tissue, that are not apparently explicable as results of 



