390 C. M. Child 



axial intestine and the development of the new branches occur 

 earHer. This difference in the rapidity of change is also exactly 

 what might be expected according to our hypothesis, for the char- 

 acteristic muscular activity and consequently the movements of 

 the intestinal contents into the branches decrease as the length of 

 the piece decreases, hence the shorter the piece, the greater the 

 change in mechanical conditions affecting the intestinal branches. 

 If the mechanical conditions are the determining factors, it follows 

 that the rapidity of degeneration must increase with decreasing 

 length of the piece. But increased rapidity of degeneration results 

 in more rapid accumulation of the products of degeneration in the 

 axial intestine and so in earlier development of the new branches. 

 This interpretation seems to me the only one possible. These 

 cases show very clearly that the factors which determine the 

 degeneration or the development of a structure are not necessarily 

 associated primarily with nutrition or its absence. Development 

 without energy is of course impossible and this energy must come 

 from nutritive material of some sort. But the mere presence of 

 the material does not necessarily determine that a given structure 

 shall develop. That, as I have endeavored to show in most of the 

 papers of this series and in others as well, is determined by func- 

 tional conditions in the widest sense. 



V THE RAPIDITY OF GENERAL INTESTINAL REDUCTION UNDER 

 DIFFERENT CONDITIONS 



Intestinal reduction in the whole body or piece proceeds with 

 very different rapidity in different cases. The rapidity of reduc- 

 tion in certain special cases has already been discussed in the pre- 

 ceding sections, but a general comparison of the various cases 

 presents certain features of interest since it shows very clearly that 

 nutritive conditions are, at least in certain cases, not the only, 

 nor even the most important, factors in determining the rate of 

 intestinal reduction. 



In the first place intestinal reduction proceeds more slowly in 

 the normal animal without food than in headless pieces of any size. 

 This is evident from a comparison of the figures. Fig. 6 repre- 



