112 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



processes. Besides these three types of processes of restitu- 

 tion there may be mentioned a fourth one, consisting in 

 what is generally called compensatory hypertrophy ; the 

 most simple case of such a compensatory process is when 

 one of a pair of organs, say a kidney, becomes larger after 

 the other has been removed. 1 Finally, at least in plants, a 

 change of the directive irritability, of so-called " geotropism " 

 for instance, in certain parts may serve to restore other 

 more important parts. 



In two of these general types of restitution, in regenera- 

 tion proper and in the production of adventitious organs, 

 the potencies which underlie these processes may be said 

 to be " complex." It is a complicated series of events, a 

 proper morphogenesis in itself, for which the potency has 

 to account, if, for instance, a worm newly forms its head 

 by regeneration, or if a plant restores a whole branch in 

 the form of an adventitious bud. 



Such generalisations as are possible about the distribu- 

 tion of complex potencies are reserved for a special part 

 of our future discussion. 



Secondary restitution is always, like ontogeny, a process 

 of morphogenesis, and therefore all the questions about 

 single formative stimuli, and about internal and external 

 conditions or means, occur again. But of course we cannot 

 enter into these problems a second time, and may only 



1 But real compensatory differentiation occurs in the cases of so-called 

 "hypertypy" as first discovered by Przibram and afterwards studied by 

 Zeleny : here the two organs of a pair show a different degree of differentia- 

 tion. Whenever the more specialised organ is removed the less developed 

 one assumes its form. Similar cases, which might simply be called "com- 

 pensatory heterotypy," are known in plants, though only relating to the 

 actual fate of undifferentiated " Anlagen" in these organisms. A leaf may 

 be formed out of the Anlage of a scale, if all the leaves are cut off, and so on. 



