PROCESS OF REPRODUCTION IN ORGANISMS. " 



in the case of the posterior region of the earthworm, which 

 produces a new posterior end at its anterior end when isolated. 



But whatever the complications, the existence of dominant 

 and subordinate parts is of great importance for inheritance. 

 The dominant part can never become anything else for it rep- 

 resents the fundamental reaction system of the species, but 

 from the subordinate parts a new dominant part may arise 

 when they are isolated from their correlation with the old dom- 

 inant part. In such cases, as I shall show elsewhere, the forma- 

 tion of the new dominant part from the subordinate part is 

 not the restitution of a missing part but the first step in the 

 formation of a new individual from the material of the sub- 

 ordinate part. The old part does not determine that a new 

 head or apical region shall arise, but this occurs in spite of the 

 old part. In general the weaker the old part the more readily 

 does the new head or apical region form and vice versa. The 

 results of my experiments soon to appear demonstrate this beyond 

 a doubt. As regards the formation of a new posterior region 

 from more anterior parts the case is quite different. The pos- 

 terior region is subordinate to regions anterior to it, consequently 

 the weaker the old part the less readily does the new posterior 

 region arise from it and vice versa. It is possible experi- 

 mentally to accelerate or even to determine the formation of a 

 new anterior region from a piece by decreasing its rate of metab- 

 olism and by the same means to retard or inhibit the formation 

 of a new posterior end. 



Secondly, there undoubtedly exists, at least for certain cor- 

 relative processes a distance-limit, a limit of effectiveness, beyond 

 which the correlative influence is ineffective. Some evidence 

 upon this point I have presented in the paper referred to. This 

 limit of effectiveness is not absolute but varies with the rate of 

 metabolism in the part where the correlative factor originates, 

 with the character of the path of correlation and with other con- 

 ditions. In various cases we can alter this limit experimentally. 

 On the other hand, the sensitiveness or receptivity of a part to 

 a correlative factor may itself vary according to conditions in 

 and about the part serving as receptor. 



From these facts it follows that the physiological isolation of 



