6 C. M. CHILD. 



in character with the experimental reproductions or regulatory 

 reproductions. Here the reproductive process is initiated by 

 complete physical isolation of a part, either through accident 

 or in consequence of violent stimulation. 



In the paper referred to above I have analyzed the concept 

 of physiological isolation and have pointed out the different 

 ways in which it may come about. It is impossible at this 

 time to go into these matters in detail but a brief review of some 

 of the chief points is essential. And first the idea of the physi- 

 logical dominance and subordination of parts requires attention. 

 Some parts of organisms are relatively dominant physiologically, 

 others relatively subordinate. In the simpler organisms, e. g., 

 the plant, Tubularia, Planaria, etc., the anterior region or the 

 apical region, the vegetative tip in the plant, the hydranth 

 region in Tubularia (Child, '090, p. 19, '096), the head region in 

 Planaria (Child, 'n/) is physiologically dominant over all 

 other parts. The question as to the nature of this dominance 

 will be considered elsewhere. 



In such cases reproduction is a relatively simple matter: 

 within certain limits any part of the organism which becomes 

 isolated from the dominant part either physically or physio- 

 logically undergoes changes which lead to the formation of a 

 new dominant part, which then controls and determines the 

 reorganization of the remainder of the piece and the result is a 

 new whole. In short, the dominant part represents physio- 

 logically the fundamental type of reaction of the specific pro- 

 toplasm. Some portion, usually the anterior or apical region, 

 of the isolated piece returns to this type of reaction and becomes 

 first of all a new dominant part. In correlation with this sub- 

 ordinate parts then develop so far as material or energy is avail- 

 able. 



In the higher organisms conditions may be more complex. 

 The organism may consist of several or many systems, more 

 or less closely correlated and each with its own dominant part. 

 Moreover, as structural characteristics become more stable 

 the capacity for regulation decreases and subordinate parts, 

 even though isolated, may be incapable of any regulation or 

 may give rise merely to new parts like themselves, as for example 



