C. M. CHILD. 



I. THE RECONSTTTUTION OF ISOLATED PIECES OF ORGANISMS. 



If we isolate physically a piece of one of the simpler organisms 

 capable of regulation, e. g., Hydra, Planaria, we know that within 

 certain limits of size and other conditions the isolated piece 

 reconstitutes itself into a new individual which possesses the 

 essential characteristics of the species. Here then is a case of 

 reproduction induced experimentally. 



But what initiates the process of reconstitution? Why does 

 the part become a w r hole? Most authorities are agreed at present 

 that the isolation of the part is the essential factor in initiation 

 of the process of reconstitution. Before isolation the part in 

 question was in physiological correlation w r ith other parts, i. e,, 

 the processes going on in them influenced it in one way or another, 

 affecting the rate, the character, the localization or the sequence 

 of the processes occurring in it. With the act of isolation all 

 these influences cease. What is the result? We see first that 

 the piece or some part of it undergoes a process of dedifferentia- 

 tion. It may lose to a greater or less extent the structural fea- 

 tures which were characteristic of it as a part or it may give rise 

 to embryonic tissue at the cut surface. Sooner or later this 

 process of dedifferentiation is succeeded by a process of re- 

 differentiation and the part gradually becomes a new whole 

 organism. 



In this process it is evident, first that the dedifferentiation is 

 the result of the isolation. So long as the piece was in correlation 

 with other parts it remained a part. After isolation it lost the 

 features which characterized it as a part. Secondly, having 

 lost these features to a greater or less extent it began to behave 

 in the manner characteristic of the protoplasm of the species to 

 which it belongs, i. e., it began to develop into a new individual 

 with the specific characteristics. The process of dedifferentiation 

 is not an assumption but an observed fact. It has long been 

 known that in plants many cells are capable of undergoing 

 dedifferentiation. In the lower animals various cells which are 

 certainly not morphologically undifferentiated are capable of 

 becoming embryonic in character and of giving rise, e. g., in 

 regulation, to various parts, and, in nature, to germ cells. These 

 cells are often regarded as indifferent or undifferentiated but I 



