Il8 HARRIET L. ROBBINS AND C. M. CHILD. 



ends. Here the difference in rate is proportionally about the 

 same as in Experiment 2, but somewhat less than in Experiment I . 



In Experiment 5 regenerated animals are compared with 

 stock animals of slightly larger size (the smallest in the stock at 

 the time) which were kept without food while the pieces were 

 regenerating, both lots being fed three times before the experi- 

 ment, and both consisting of entire animals. Here again the 

 regenerated animals show a higher rate of CO% production than 

 the slightly larger stock animals. 



A few other experiments performed by one of us and in some 

 cases also by students in the laboratory, are briefly mentioned 

 here without tabulation of the data. It has been found, for 

 example, that the degree of increase in both susceptibility and 

 COz production occurring in regeneration depends upon the 

 degree of reorganization which occurs. Consequently the smaller 

 the piece in relation to the size of the body from which it is taken, 

 the greater the amount of increase in susceptibility and CO%. 

 Similarly in natural fission the posterior piece is not only smaller 

 than the anterior but develops a new head at the anterior end 

 and a prepharyngeal and pharyngeal region by reorganization 

 and redifterentiation within the piece, while the anterior fission 

 piece develops merely a new posterior end. In the animal 

 developed from the posterior piece susceptibility and COz 

 production show a marked increase while in the anterior animal 

 the only marked change in susceptibility is a slight increase in 

 the posterior region, where reorganization and growth have 

 occurred and the increase in CO 2 production is either slight or 

 inappreciable. Allen ('19) has recently recorded somewhat 

 similar results as regards oxygen consumption, an increase 

 occurring in the posterior, but not in the anterior product of 

 fission. 



It has also been determined by one of us that susceptibility 

 to lack of oxygen increases during the development of a new 

 individual from a piece, the susceptibility of the new individual 

 about two weeks after section of the piece, being distinctly higher 

 than that of well fed animals of the same size and about the 

 same as, or slightly than that of animals of the same size, kept 

 without food for the same length of time as the regenerating 



