STUDIES ON THE DYNAMICS OF MORPHOGENESIS 309 



deaths occur among the one-fourth, one-sixth and one -eighth 

 pieces: in the twelfth pieces the deith rate is low and is con- 

 fined to the pieces from the middle region of the body. In the 

 sixteenth pieces the death rate is distinctly higher, though 

 even here deaths do not occur among the pieces from the terminal 

 regions. Tables 2, 3 and 4 show no deaths at all, but in 

 table 5, where the pieces are smaller than in tables 2 — 4, deaths 

 again appear and are more frequent in the smaller than in the 

 larger pieces. Evidently the possibility of maintaining an inde- 

 pendent existence is a function of the size of the piece. 



The presentation of further data must precede any extended 

 consideration of this factor of size. At present it is desired to 

 call attention only to certain points. 



In the first place, the change from wholeness to partial struc- 

 tures with decreasing size suggests that below a certain limit of 

 size something necessary for wholeness is lost. What this some- 

 thing is will appear more clearly later. 



The change in the method of regulation with decrease in size 

 indicates a change in the physiological condition of the cells 

 near the cut surface. In general we find that under like con- 

 ditions redifferentiation occurs in parts which ire more closely 

 similar to the part removed, regeneration in parts less similar 

 (Child, '06a) ^ In other words, in the former case redifferentiation 

 takes place more rapidly and the stimulus to regeneration is less 

 than in the latter. If my conclusions are correct on this point 

 then it is evident that with decreasing length of the piece the 



^Various conditions alter the relation between redifferentiation and regenera- 

 tion. For instance, as Morgan observed, starvation increases the relative amount 

 of redifferentiation. Various depressing agents, such as anesthetics, also increase 

 the relative amount of redifferentiation, until in extreme cases regeneration, in 

 the formation of a head for example, is almost absent. In all cases there is evi- 

 dently an inverse physiological correlation between the two forms of reaction. 

 The formation of new tissue is retarded in the absence of nutrition or in the 

 presence of agents which retard the oxidations, consequently the process of redif- 

 ferentiation proceeds relatively more rapidly than otherwise. In general the 

 result in any given case is determined by the relative rapidity of the two processes. 

 All conditions which retard the rapid proliferation of cells and the growth of new 

 tissue, as well as all conditions which accelerate redifferentiation (e. g., physio- 

 logical likeness) will increase the relative amount of redifferentiation in a given 

 case, and vice versa 



