206 Cc. M. CHILD 
the plant, in consequence of the removal of other vegetative tips, 
the formation of a hydranth from cells of the stem of Tubularia, 
etc. 
The difficulty les in distinguishing qualitative from quantita- 
tive regulations. In living organisms the two are evidently very 
closely associated, and probably in every regulation which we 
can observe directly both are concerned. And in the final analy- 
sis the question of the relation between quality and quantity in 
general is involved, though this is scarcely a biological problem. 
As regards the further classification of the regulatory transfor- 
mations, I think that at present the most satisfactory basis for 
classification is the comparison of the new system with that exist- 
ing before regulation. The following division of this group of 
regulations is therefore suggested: 
Progressive transformation: the regulatory formation of a sys- 
tem possessing a greater degree of complexity, more varied locali- 
zation of structure and function and consequently more varied 
correlation than the system existing before regulation. 
Regressive transformation: the regulatory formation of a sys- 
tem of simpler character than the preéxisting. 
Transgressive transformation: the regulatory formation of a 
system which cannot be distinguished as more or less complex, 
but merely as different from the preéxisting. 
Suh a classification serves merely to suggest the various pos- 
sibilities. As our knowledge of the processes concerned in the 
changes of the organic system increases, the basis of classification 
will change. Without doubt many progressive transformations 
occur in normal development. The adult organism is certainly a 
more complex and qualitatively different system from the blas- 
tula, and we know that correlative factors have been concerned 
in the changes in many parts. A regressive transformation occurs 
when a part undergoes dedifferentiation in consequence of altered 
correlation, as in various cases where cells which give rise to new 
parts first lose their old differentiation. 
The group of transgressive transformations possesses little 
more than a conventional significance, since it is based upon 
difference from the normal which is essentially merely the usual 
