118 • C. M. CHILD 



or less dedifferentiation and growth, but the greater the degree 

 of stimulation of the region y the greater the degree of inhibi- 

 tion of these changes in x and wice versa. As experiments al- 

 j'eady described have shown, this inhibiting influence of y upon 

 .T depends in some way upon the relative rates of metab- 

 oHsm in y and x. The dedifferentiation and division of the 

 cells at X in reaction to the wound and the absence of more 

 anterior parts brings about a progressive increase in metaboUc 

 rate in these cells and the stimulation of y also determines a 

 temporary increase of rate in its cells. The stimulation of y 

 undoubtedly occurs chiefly through the nervous system and 

 constitutes what we may call a functional stimulation, i, e, it 

 tends to maintain and intensify both the dynamic and chemical 

 correlative conditions which determine and maintain the dif- 

 ferentiation of the cells affected by it. The region x, however, 

 is subjected to conditions which bring about dedifferentiation 

 and a return or an approach to an embryonic condition, in 

 other words the cells react to the absence of correlative factors 

 which previously determined and maintained their differentiation. 

 It is not difficult to see that these two factors are opposite 

 in character, the one tending to maintain the existing differentia- 

 tion and the other to destroy it. If the functional stimulation 

 of y is sufhcient, i.e., if the metaboUc rate in y is sufficiently 

 high as compared with that of x, the process of dedifferentiation, 

 and renewed di\ision and growth of the cells of x is retarded or 

 largely inhibited and the cells merely close the wound and dif- 

 ferentiate as the correlative conditions originating in adjoining 

 parts of y determine. If, on the other hand, the functional 

 stimulation of y is slight the cells of x are but little affected by 

 the correlative conditions in y and are therefore free to react to 

 the absence of correlative factors from more anterior levels by 

 dedifferentiation, division and growth. Under these conditions 

 a mass of new embryonic tissue is formed and this gives rise to 

 a new apical end or first of all to a new cephalic ganglion, this 

 being, as I have pointed out (Child, '11 c, '13 b, '15 b, pp. 96- 

 116, 188-192), the fundamental action of the specific pro ooplasm 

 and independent, at least ir its earlier stages, of correlative 



