112 INDIVIDUALITY IN ORGANISMS 



condition. The cells of y^ however, merely undergo a 

 temporary increase in metabolic rate. The region a: is a 

 small groups of cells undergoing dedifferentiation, while y 

 represents a considerable portion of a fully developed 

 individual with established relations of parts and spe- 

 cialized nerves which are much more efficient than 

 embr^^onic protoplasm as conducting paths. The region 

 X originally has a higher metabolic rate than y, because 

 it represents a more apical level in the gradient, and its 

 rate rises still farther as it begins to dedifferentiate. 

 The facts of experiment indicate that in order to produce 

 a new head rate x must not merely be higher but much 

 higher that rate y. The relation between x and y 

 is evidently this: if rate x is sufficiently above rate y, x 

 develops independently of y into a head and dominates 

 y, while otherwise y dominates a: to a greater or less ex- 

 tent and so retards or inhibits head-formation, and the 

 various forms between normal and headless condition 

 are produced. 



This relation ^^^ can be altered in various way-s: 

 by means of dilute narcotics it is possible according to 

 the method of use either to decrease the stimulation 

 in y resulting from section or to delay the reaction in x 

 until after the increased rate in y has largely or wholly 

 disappeared, or finally the relation may be altered by the 

 more rapid and more complete acclimation of the young 

 cells at X as compared with the older cells of y (see 

 pp. 51, 52). In pieces such as c. Fig. 57, where under 

 ordinary conditions x and y are, so to speak, evenly 

 matched in the struggle for dominance and the head- 

 frequency is low, all these methods increase the head- 

 frequency, because the relative increase in rate of x as 



