Compensatory Regulation. 97 



wise in the three-leaved system after removal of one of the asym- 

 metrically placed leaflets the two remaining leaflets tended to take 

 up a position so as to form a symmetrical two-leaved system. 

 From the position reactions it is evident that the parts of the 

 normal compound leaf are exerting a continual influence upon 

 each other which when resolved into its resultants gives rise to a 

 configuration very definite for a given species. The removal of 

 one of the parts changes the whole system of reactions, and we have 

 a tendency toward the formation of a new stable symmetrical system, 

 with one less leaflet than the original number, the completeness of 

 the new symmetry being only limited by the rigidity of the leaflets. 



In Ophioglypha we have a radial system in which the removed 

 arms are regenerated. The experiments on the rate of regenera- 

 tion bring out the presence of an unsuspected interaction between 

 the arms which must naturally be correlated with some interac- 

 tion present in the perfect, unmutilated animal. The data of the 

 experiments show that (leaving out of consideration the cases 

 where all five arms are removed and which cannot be used because 

 of the early death of the animals) the rate of regeneration of an 

 arm is greater the greater the number of other arms removed at 

 the same time. This indicates an interesting interaction of the 

 arms upon each other for the presence of unremoved arms seems 

 to retard the rate at which the removed ones are regenerated, for 

 it is not probable that the increase in rate in the one case is due 

 entirely to the increase in stimulus to regeneration produced by 

 the added injuries. 



The two members of a pair of appendages in bilateral animals 

 have been shown by the present experiments to have a profound 

 influence upon each other. 



In those Serpulids, for example, which have one large functional 

 and one small rudimentary operculum it has been shown that either 

 organ originally has the potentiality of developing into a functional 

 operculum, which is to be developed in this way, depending upon 

 the matter of an early start. When one side gets a start over the 

 other the development of the latter is restricted to a rudimentary 

 stage, while the former develops to a full functional size. Also, 

 when the functional operculum is removed its restricting influence 

 being removed at the same time, the rudimentary operculum 

 immediately develops into a functional one, which in turn restricts 

 the developing new bud of the other side. When both develop at 



