DYNAMICS OF MORPHOGENESIS 125 



lb-pieces (figs. 27 and 28) and anterior regulation in the ^a-pieces 

 (fig. 29) is less affected than in the ^fe-pieces (fig. 30) and in these 

 less than in the ^c-pieces (fig. 31). In short the same gradient 

 appears in these experiments as in those with alcohol. If, as has 

 been suggested, KCN retards the oxidation processes the results 

 of the experiments suggest the existence of a gradient in the rate 

 of the oxidation processes along the axis. As will appear later 

 there is very strong evidence along other lines for the existence 

 of such a gradient. 



Incidentally two other points of interest concerning these 

 pieces may be noted: first, in the KCN the development of the 

 optic pigment cups is more completely inhibited than that of the 

 unpigmented optic areas. In the ia-pieces the optic pigment 

 cups are represented by small dots, while the unpigmented areas 

 are much more nearly the usual size; the same condition exists in 

 those ^6-pieces which develop eyes (fig. 28). In the ^a-pieces 

 this differential effect is still more striking for here the pigment 

 cups are absent, though the unpigmented areas are well marked 

 (fig. 29). 



Second, the differentiation of the sensory unpigmented areas 

 of the auricles is less completely inhibited than the outgrowth of 

 the auricles. In the la-pieces (fig. 26) there is a barely appre- 

 ciable outgrowth, but the sensory areas are well developed and in 

 the ^a-pieces (fig. 29) the sensory areas appear without any trace 

 of outgrowth. These results show some of the possibilities of 

 analysis of regulatory morphogenesis. 



3. Experiments with temperature 



Series 310, 311, 314. January 9, 1911. These series show the 

 effect of different temperatures upon the regulatory processes at 

 the posterior ends of short anterior pieces. The pieces used in- 

 cluded the head and the short portion of the body anterior to the 

 level 1 in figure 32; all were cut from well-fed animals 16 to 18 mm. 

 in length from the same stock. Pieces of this size and character 

 were chosen because they represent in a sense a critical length for 

 this region of the body and for medium temperatures, i.e., at 

 temperatures of 18° to 22°C. such pieces sometimes give rise to 



