EXPERIMENTAL MORPHOGENESIS 111 



of all the potencies for the primary processes of ontogeny 

 proper. Let us first add a few words about the concept 

 of " secondary restitution ' and about the distribution 

 of secondary potencies in general. 



Primary ontogenetic processes founded upon primary 

 potencies may imply regulation, or more correctly, restitu- 

 tion in many cases : so it is, when fragments of the blastula 

 form the whole organism, or when the mesenchyme cells 

 of Echinus reach their normal final position by an attraction 

 on the part of specific localities of the ectoderm in spite 

 of a very abnormal original position enforced upon them 

 by experiment. In these cases we speak of primary 

 regulations or restitutions ; disturbances are neutralised by 

 the very nature of the process in question. We speak 

 of secondary restitution whenever a disturbance of organ- 

 isation is rectified by processes foreign to the realm of 

 normality ; and these abnormal lines of events are revealed 

 to us in the first place by the activity of potencies which 

 remain latent in ontogeny proper. 



We know already that a certain kind of secondary 

 restitution has been discovered lately, very contradictory 

 to the theoretical views of Weismann ; the process of 

 restoration being carried out not by any definite part of 

 the disturbed organisation, but by all the single elements 

 of it. The problem of the distribution of secondary 

 potencies in these cases of so-called " re-differentiation ' is 

 to form our special study in the next chapter. In all 

 other cases restoration processes start from specific localities ; 

 if they occur on the site of the wound which caused the 

 disturbance, we speak of regeneration ; if they occur at 

 some distance from the wound, we call them adventitious 



