Compensatory Regulation. 7 



metrically placed leaflet the resulting two-leaved system tends to 

 be symmetrical with respect to the petiole. This shows very 

 definitely that the normal symmetrical palmate leaf has a definite 

 configuration as a result of the interaction of its units and that the 

 manner of this interaction may be revealed by the removal of a 

 unit, an operation which brings about a yie%v mode of interaction 

 leading to a new resultant state of equilibrium. 



Likewise after such an operation, which is performed at an early 

 stage before the leaflets have fully unfolded, the remaining leaflets 

 do not attain their full normal size, the average decrease for the 

 leaflets of the three species being 6.8 per cent of the normal length. 

 These changes in position and length for the Virginia Creeper are 

 shown in the accompanying figure. (Fig. i.) 



In the following sections the experiments have to deal with more 

 complicated cases because there is a regeneration of a new organ 

 or organs in place of the old, and the changes in the system are 

 the result not only of the interactions of the uninjured parts but 

 also of these upon the regenerating part and in turn of the latter 

 upon the former. 



II. THE RATE OF REGENERATION OF THE ARMS IN THE BRITTLE- 

 STAR, OPHIOGLYPHA LACERTOSA.^ 



I. Introduction. 



In this section we have a case of evident influence of organs 

 situated aivay from a regenerating surface upon the character of 

 the regeneration at that surface. The mfluences exerted by the 

 regenerating organ or organs upon the character of the uninjured 

 organs, or the changes produced among the unmjured organs 

 themselves by the new interactions resulting from the new con- 

 ditions, were not studied because the material was evidently 

 unsuitable for that purpose. The experiments to be described 

 are, therefore, concerned entirely with the rate of regeneration of 

 the arms as influenced by the number of arms removed. Inci- 

 dentally the variation of the rate of regeneration of the arms with 

 the size (i. e., age [ .^]) of the animal must be considered. 



^The principal results of this section were given in a preliminary paper already mentioned. (Zeleny, 



