Studies on Regulation. IV. lOi 



tinct from any irritation due to a wound, for they continue after 

 the wound has closed and new tissue has appeared. There is 

 no doubt, I think, that a modification of the motor stimuU occurs 

 in the absence of a part important to locomotion. 



The outgrowth of new tissue from the cut surface is probably, 

 in its earlier stages, the result of the alteration in local conditions 

 consequent upon the removal of a part. But the position of the 

 new tissue, i. e., its connection with a particular part of the old 

 body determines the conditions to which it is subjected in connec- 

 tion with the functional activities of the old differentiated parts. 

 As differentiation in the new tissue proceeds, motor activity ap- 

 pears and soon the movements of the new part are coordinated 

 more or less completely with those of adjoining old parts. Thus 

 the conditions to which the new part is subjected become similar 

 to those which were present in the part removed. These condi- 

 tions or some of them are undoubtedly formative factors in many 

 cases. In Stenostoma (Child, '02, '03) the development of the 

 tail depends in large degree upon their presence. 



Now when the new part first shows characteristic coordinated 

 motor activity it is much smaller than the part removed, yet func- 

 tionally it supplies the place of the other, though at first very 

 imperfectly. But the smaller the size and the more imperfect 

 the formation of the new part, the greater the activity, i. e., the 

 "attempt" of the animal to use it. Thus the new part is visibly 

 more active than the old and if we admit that the conditions con- 

 nected with this activity are "formative factors" it is easy to see 

 why in a starving piece the new part continues for a longer or 

 shorter time to increase in size at the expense of the old tissue. 



As the new part increases in size and its coordinations become 

 more perfect the degree of motor activity decreases, approaching 

 that of the old parts. The extent of regeneration in starving 

 pieces is probably determined by the relative functional activity 

 of the new and old parts. As long as the more intense metabol- 

 ism of the new part enables it to deprive the old part of material, 

 so long will it continue to increase in size. It is also probable 

 that the old tissue gives up material less and less readily as the 

 encroachments continue. The final result depends on the condi- 

 tions of the individual case. 



