CO 2 IN RELATION TO REGENERATION IN PLANARIA. 1 09 



changes in oxygen consumption in two other species of Planaria 

 during the early stages of starvation. It is evident that the 

 rapid decrease in CC^ production and oxygen consumption during 

 the early stages of starvation is due in large measure, if not 

 wholly, to the decrease in functional activity of the alimentary 

 tract in the absence of food newly ingested. In the light of all 

 these facts the reason for the use in these experiments of animals 

 which have been starved a few days is evident. The length of the 

 period without food is given in each experiment: in no case is it 

 long enough to produce any marked reduction in size or other 

 changes except those in the alimentary tract. 



Since the purpose of these experiments is to determine whether 

 differences and changes in susceptibility following section are 

 paralleled by differences and changes in CO 2 production, the 

 size of animals and pieces used and the regions of body included 

 are those which show the most definite and characteristic differ- 

 ences and changes in susceptibility. The experimental material for 

 the data presented in Table I. was prepared as follows: animals 

 sixteen to eighteen mm. were selected from well fed laboratory 

 stock, those which had recently undergone fission being excluded, 

 were kept without food for several days (see Table I.) and were 

 then cut into pieces as indicated in Fig. I, piece C being cut so 

 that the greater part of the pharynx is separated from its attach- 

 ment and is extracted from the pharyngeal pouch, i.e., piece C 

 contains a part of the pharyngeal pouch, but no portion of the 

 pharynx. Pieces A and C were used in the experiments as repre- 

 senting respectively the most anterior and the most posterior 

 portion of the first or chief member or zooid in animals of this 

 size (Child, 'lib). In the intact animal the susceptibility of the 

 region corresponding to piece A is very much greater than that of 

 the region corresponding to piece C. Immediately after section 

 the susceptibility of piece A shows either a slight increase or no 

 marked change, while the susceptibility of C is increased to such a 

 degree that it is equal to or even greater than that of A (Child, 

 '14). The region B between A and C is intermediate both as 

 regards original susceptibility and the changes following section 

 and is not used in these experiments. The increase in suscepti- 

 bility following section, which is most marked in the C-piece is 



