AGE DIFFERENCES IN METABOLISM OF PLANARIA. 



TABLE III. 



399 



COMPARISON OF THE RATE OF OXYGEN CONSUMPTION OF SEXUALLY MATURE 



INDIVIDUALS (15 MM. OR LONGER) WITH THE SEXUALLY PRODUCED 



YOUNG (5 MM. OR LESS) OF Planaria maculala. 



Four Lots of Sexually Mature Individuals, Collected July 10; First Three Lots 



Tested July n; Fourth Lot Kept Until August n, with Frequent Feedings, 



Last Feeding August 8, Tested August n. Temp. 20 C. 



Three Lots of Sexually Produced Young; Young and Capsules Collected July 10 



Fed at Frequent Intervals; Last Feeding of Lots i and 2, July 28, Tested July 



31; Lot 3, Last Feeding August 8, Tested August n. Temp. 20 C. 



V. CONCLUSIONS. 



These experiments show that small or young planarians con- 

 sume oxygen at a faster rate per unit weight than larger or older 

 ones. As already stated, the carbon dioxide production is also 

 inversely proportional to the size of the worms. It is true that 

 experiments of this kind do not and cannot prove that the proto- 

 plasm of young animals actually has an intrinsically higher 

 metabolic rate than that of older ones, for the reason that it is 

 impossible to discover what part of the weight of an animal is 

 active protoplasm and what part inert material. Nevertheless 

 there cannot be any reasonable doubt that the metabolic rate 

 is inversely proportional to age. It would be difficult to suggest 

 any other explanation for many of the facts cited in this paper, 

 namely, for the faster rate of respiration, faster heart beat, and 

 more rapid rate of other physiological activities of young as 



