[51] T. H. Morgan is very right in stating that, in regeneration, the “obstacle” itself is newly formed by the mere process of healing, previous to all restitution, and that true restitution happens all the same. But where then is the stimulus to be found? There is another rather simple theory of the “Auslösung” of restitutions,[52] which starts from the phenomena of compensatory hypertrophy and some occurrences among plants. The removal of some parts of the organism, it is said, will bring its other parts into better conditions of nutrition, and therefore these parts, particularly if they are of the same kind, will become larger. Granted for the moment that such a view may hold in cases when one of a pair of glands becomes larger after the other has been removed, or when pruning of almost all the leaves of a tree leads to the rest becoming larger, it certainly must fail to explain the fact that in other cases true *new* formations may arise in order to restore a damaged part, or that the latter may be regenerated in its proper way. For *merely quantitative* differences in the mixture of the blood or of the nourishing sap in plants can never be a sufficient reason for the highly typical and *qualitative* structure of newly-formed restitutions. And even in the most simple cases of a mere increase in the size of some parts, that is, in the simplest cases of so-called compensatory hypertrophy,[53] it is at least doubtful, if not very improbable, that the compensation is accomplished in such a purely passive way, because we know that in other cases it is usually the growth of the young parts that actively attracts the nourishment: there is first differentiation and growth, and *afterwards* there is a change in the direction of the nourishing fluids. [52] I merely mention here the still “simpler” one--applicable of course to regeneration proper exclusively--that for the simple reason of being “wounded,” *i.e.* being a surface open to the medium, the “wound” brings forth all that is necessary to complete the organism. [53] That compensatory hypertrophy cannot be due to “functional adaptation”--to be analysed later on--was proved by an experiment of Ribbert’s. Compensation may occur before the function has made its appearance, as was shown to be the case in the testicles and mammae of rabbits. (*Arch. Entw. Mech.* 1, 1894, p. 69.) The process of true regeneration, beginning at the locality of the wound itself, has been shown by Morgan, even as regards its rate, to occur quite irrespectively of the animal being fed or not.[54] There could hardly be a better demonstration of the fundamental fact that food assists restitution, but does not “cause” it in any way.