DYNAMICS OF MORPHOGENESIS 151 



direction demonstrates clearly enough that the relation between 

 this capacity and the axial gradient is not simple but complex. 

 The possibiHty of altering and controlhng experimentally the 

 regulatory capacity of pieces, not only as regards rate and size 

 of parts but also as regards the presence or absence of their most 

 important morphological characteristics, the head, the eyes, the 

 auricles, the pharynx and the posterior end points to a promising 

 field of investigation. Moreover, since the experimental factors 

 which accomplish these results are such as influence the dynamic 

 processes in the pieces and since in my own experiments it is 

 known that their effect is primarily quantitative, it is not too much 

 to say that these experiments throw some Ught on the problem of 

 the dynamics of morphogenesis and inheritance. And finally it 

 is evident that we must interpret regulatory phenomena in terms 

 of dynamic processes rather than in terms of morphology. 



IV. SUMMARY 



1. When pieces of a single zooid of Planaria dorotocephala 

 undergo regulation in dilute anesthetics (alcohol, ether, chlore- 

 tone) the degree of retardation or inhibition of morphogenesis 

 increases posteriorly along the axis of the piece. The formation 

 of a head may occur under conditions which inhibit all other regu- 

 latory processes and the head and pharynx may form under con- 

 ditions which inhibit the formation of the posterior end. 



2. Very dilute solutions of KCN give results similar in general 

 character to those obtained with alcohol, etc., but more striking 

 in that the axial factor appears more clearly. 



3. Experiments at different temperatures also show the exist- 

 ence of the axial factor, though less clearly than the anesthetics 

 and KCN. Starvation and the presence of metabolic products 

 of Planaria in the water likewise give essentially similar results. 



4. The axial gradient also appears in the different effects of 

 KCN and other depressing agents upon the process of head-for- 

 mation at different levels of the body. The effect of the depress- 

 ing agent is not only different in degree at different levels but 

 under certain conditions may be different in direction Cyanide, 



