50 PATTEN. (Vo. XII. 
as due to the fact that there is greatest tension along those 
lines, Ax., and less growth power to resist it, because the 
tissues at those points are oldest, and have already exhausted 
more of the inherent powers of growth than at 7. 
It may not be venturing too far to claim for this principle still 
further applicability ; for example, in explaining the more pro- 
found and remote physiological differences between the anterior, 
middle, and posterior regions of the body. Or rather, it would 
be better to say that this morphological law is the formal 

Fic. 5. 
expression of the fact that differential growth tension has fixed 
the posterior, middle, and anterior regions of the body as the 
seats, respectively, of constructive, elaborative, and destructive 
physiological processes. But it will not do to press this 
thought too far, certainly not without a precise statement of 
the way it is to be applied. 
It would also be important to determine whether there is 
any relation between these laws of growth and decline and the 
different powers of regeneration shown by various regions of 
the body, and in this connection we would recall the difference 
so manifest in this respect between the head and tail region. 
If such were, indeed, the case, there might be some foundation 
for the supposition that growth and regeneration are associated 
