AGE DIFFERENCES IN METABOLISM OF PLANARIA. 395 



induced by Dr. Child in this laboratory), but maintains itself 

 by means of asexual fission. In fission, the posterior portion 

 of the body pulls away from the anterior end, regenerates a head 

 and becomes a complete small worm. Such small worms cor- 

 respond in all tests which have been made upon them, to young 

 worms in species reproducing sexually. 



Six experiments were performed in which the rate of oxygen 

 consumption of such small worms, under 10 mm. in length, was 

 compared with that of large worms, over 20 mm. in length. In 

 all cases, both large and small individuals were taken from the 

 same stock and had been kept under the same conditions previous 

 to the experiment. No worms showing signs of recent fission 

 or regeneration were used. The heads were cut off the day 

 before the test was made in order to eliminate movement. Two 

 successive determinations of the oxygen consumption of each 

 lot of worms were usually made, the worms were then weighed, 

 and the oxygen consumption per two hours per 0.5 grams weight 

 then calculated. 



The method of determining the rate of oxygen consumption 

 and the method of weighing have been described in previous 

 papers (Hyman, '190, '19^). 



The results of the six experiments are given in Table I. In all 

 cases the smaller worms consume more oxygen per unit weight 

 per unit time than the larger ones. The per cent, difference 

 ranges from 18 to 55, and closer inspection of the table reveals 

 that the amount of difference is correlated with the length of 

 time which has elapsed since the last feeding. In experiment 4, 

 where the small worms respire but 18 per cent, more than the 

 large ones, only two days had elapsed since feeding, while in the 

 other experiments, where three or four days had passed since 

 feeding, the difference is greater. As shown in a preceding paper 

 (Hyman, 'i9&), feeding greatly increases the rate of oxygen 

 consumption by stimulating the digestive tract. Since the 

 digestive tract is more extensive in large than in small individuals, 

 the difference between such individuals is decreased by feeding. 

 As I did not perform any experiments with worms deprived of 

 food for longer than four days, I do not know whether further 

 starvation would increase the difference between small and large 



