Physiological Basis of Restitution of Lost Parts 493 



esses are, I believe, interpretable according to the symbiotic 

 theory, and the relations of regeneration and morphallaxis to the 

 degree of specialization of the parts which Child has elaborated, 

 are, in fact, exactly what the theory would lead us to expect '* 

 (Holmes '07, p. 427). 



Here Holmes fails absolutely, so far as I can see, to explain how 

 and why equilibrium will be maintained. Certainly the "pro- 

 gressive modifications" resulting from the removal of ^ cannot 

 bring the system back to its original condition: they must lead 

 either to destruction of the system, or rather of the parts of it 

 which remain, or else to a new condition of equilibrium different 

 from the old. How does Holmes know that "functional equilib- 

 rium would then be maintained by working over the organism 

 so that all the parts were adjusted to functioning on a smaller 

 scale V What factor in the parts remaining compensates for the 

 "progressive modifications" resulting from the loss oi A 1 Why 

 should there be any compensation .^ To none of these questions 

 does Holmes' hypothesis give any answer. 



According to the symbiotic theory as Holmes has presented it, 

 the removal of a part is, at least in many cases, analogous to re- 

 moval of a quantity from one side of an equation without change in 

 the other. It is obvious that such procedure alters the value of 

 one side of the equation in all cases except where the quantity 

 removed is equal to zero. 



In short I believe that Holmes' theory of regulation overlooks 

 the most essential feature in the process of replacement of a part 

 removed. This feature is the qualitative functional totipotence 

 of the remaining parts after rem.oval of the part in question. In 

 other words, a part which has been removed cannot be replaced 

 unless something remains after its removal which plays its part 

 functionally in some degree. According to Holmes' theory its 

 place is taken by undifferentiated tissue, which is forced to develop 

 into something hke the part removed by the influence exerted 

 upon it by other parts. But this undifferentiated tissue cannot 

 exert the same influence on other parts as was exerted by the 

 part removed. Moreover it is difficult to understand how undiffer- 

 entiated tissue whose differentiation is held in check by the other 



