Ri'gnwrdtion as Funrfional Adjiistnieut 429 



started in the right direction, or something else than the missing 

 organ would be produced. That cases of heteromorphosis some- 

 times occur might be interpreted as the result of such failures. 

 But the comparative rareness of heteromorphosis makes me sus- 

 pect that the beginnings of visible differentiation that fre(|uently 

 appear at the tips of regenerating organs do not occur without 

 any relation to the basal part. The fact that, with few exceptions, 

 such as the failure to regenerate the intermediate segments of the 

 appendages, etc., the whole organ, nothing more nor less, is regen- 

 erated, and forms a congruent union with the basal part, is indica- 

 tive of close interaction of the various parts of developing organ 

 with the body of the organism at all stages of the process. 



I am inclined to think that neither centrifugal nor centripetal 

 differentiation, expresses the entire truth of the matter, but that 

 the new part differentiates as a whole, much as organs do in embry- 

 onic development, and at all times in intimate functional relations 

 with the old part, differentiation becoming accelerated in one part 

 or another, according to special conditions. If differentiation 

 began at the tip of the rudiment of an organ, and proceeded cen- 

 trally, the whole might be differentiated before the body was 

 reached, leaving a mass of unused tissue between; or differentia- 

 tion might reach the body before all the immediate parts w^ere 

 produced. If differentiation proceeded in the reverse direction, 

 similar imperfections might arise. We must look upon a regen- 

 erating mass of tissue as one in which incipient developmental 

 tendencies are proceeding in various ways, modifying each other, 

 and gradually working into a condition of physiological equilib- 

 rium with the basal part and with the environment before much 

 outward evidence of differentiation makes its appearance. It 

 is probable that the main elements of a regenerating appendage 

 of an arthropod, for instance, are blocked out before any external 

 marks become visible. Even during the early stages of prolifera- 

 tion of the cells of the regenerating appendages, it is not improb- 

 able that incipient differentiations are becoming established. And 

 the basal part notwithstanding the fact that the visible differen- 

 tiation may take place in a centripetal direction, may exercise a 

 guiding influence at all times over the regeneration of the part, 



