no 



HARRIET L. ROBBINS AND C. M. CHILD. 



A 



B 



C 



temporary and after six to eight hours is in course of disappearance 

 and sooner or later (12 to 24 hours under ordinary conditions) 

 the susceptibility of the piece becomes about the same as or a 

 little less than that of the corresponding regions in the intact 

 animal. These temporary changes in susceptibility indicate 

 that the pieces have been stimulated by section, anterior pieces 

 least, posterior pieces most, and that the condi- 

 tion of excitation disappears after a few hours. 

 It has been suggested elsewhere (Child, '14) 

 that the difference in the degree of stimulation 

 in anterior and posterior pieces results from the 

 greater dependence of the more posterior regions 

 upon impulses from regions anterior to them, so 

 that when the paths of these impulses are cut 

 the condition of the more posterior levels is 

 more affected than that of the anterior levels. 

 This is in agreement with the observations of 

 various investigators concerning the difference 

 in intensity of reaction in many animals between 

 levels anterior and those posterior to a trans- 

 verse cut. 



The region of the body posterior to C in Fig. 

 I is not used in the tabulated experiments be- 

 cause it consists of one or more zooids indicated 

 by differences in physiological condition (Child, 

 '10, 'nc). Since the number of these posterior 

 zooids differs in different animals and no mor- 

 phological boundaries are visible, pieces from 

 the same levels of this region in different ani- 

 mals are not always strictly comparable physio- 

 logically and therefore merely complicate the 

 experimental data. 

 Each experiment on CO 2 production in the pieces A and C 

 consists essentially in determining the rate of change in pH, 

 once as soon as possible after section and again several hours 

 later, of one lot of ^.-pieces and one of C-pieces, consisting of 

 thirty to fifty pieces each and of as nearly as possible equal weight, 

 in equal volumes of indicator solution at a constant temperature 



FIG. i. 



