328 C. M. CHILD. 



under as nearly as possible identical conditions of light and 

 temperature. 



Two series of experiments are given here. In the first the 

 pieces included the region between the lines 2 and 3, Fig. I, 

 fifty pieces for stimulation (I) and fifty for control (II) being 

 taken from similar worms. 



Teratoph- Terato- Anoph- 



Normal. thalmic. morphic. thalmic. Headless. Dead. 



I o 28 8 32 32 o 



II o 8 8 26 58 o 



The second series consists of pieces including the region be- 

 tween the lines 3 and 4 in Fig. I and from the same worms as 

 the first. These pieces, being posterior to those of the first series 

 and of approximately the same size produce heads less frequently. 

 As in the first series, fifty pieces were used in the stimulated set 

 (I) and fifty in the control (II). 



Teratoph- Terato- Anoph- 



Normal. thalmic. morphic. thalmic. Headless. Dead. 



1 4 10 2 18 64 2 



II O 6 2 12 80 o 



The two pieces which produced normal heads in the stimulated 

 set of this series were undoubtedly pieces which included the 

 anterior end of the second zooid : the presence of this region even 

 at the posterior end of a piece increases greatly its head-forming 

 capacity. In both series the effect of stimulation appears un- 

 mistakably in the increased capacity for head formation. With- 

 out doubt it is not the actual performance of the movement itself 

 but the stimulation which is the important factor. Stimulation 

 means increase in the rate or intensity of the dynamic processes 

 in the piece and this appears in increased and altered formative 

 capacity. I believe that these and other similar experiments 

 to be described elsewhere establish and confirm against all ob- 

 jections my position that the process of regulation is essentially 

 a' dynamic, or as I have often called it, a "functional" process 

 or complex of processes. 



7. The Morphogenic Effect of Quantitative Changes in Conditions 



in General. 



In the temperature, nutrition and stimulation series the exper- 

 imental conditions differ quantitatively from those of the control. 



