The Metabolic Gradient and its Applications

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Abstract
1. In Nereis virens the rate of carbon dioxide discharge for the whole worm is roughly 0.01 milligram of gas per gram of worm per minute. In similar terms the rate for the mid-trunk is a little over 0.01 milligrams and that for the head and tail regions about half of this rate. 2. In Planaria metadata large worms (87 mgm.) show a lower rate of carbon dioxide discharge (0.0050 mgm. per gram of worm per minute) than small ones (55 mgm.) (0.0069 mgm. per gram of worm per minute). Also normal worms have a lower rate (0.0050 mgm.) than cut worms (0.0063 mgm.). Planarians cut transversely into halves, quarters or sixths show in such fragments so uniform a rate of carbon dioxide discharge that there is no reason to believe that the rate is really different in different parts. 3. In the actinians Sagartia luciae and Metridium marginatum the rate of discharge of the oral halves is indistinguishable from that of the aboral halves and these two rates are very close to the rates of the animals as wholes. 4. These results point to the absence of the assumed metabolic gradients in Nereis, Planaria and the actinians. 5. Hyman's results on annelids with the susceptibility method were obtained on Nereis but are believed to be due to differential penetration and are not accepted as a proof of a metabolic gradient. Hyman and Galigher's results on annelids involve a misuse of the Winkler method. Shearer's results on earthworms apply only to the head and tail ends and should have been supplemented, to be conclusive, with determinations for the mid-trunk. 6. Metabolic gradients if present are not factors in morphogenesis but are at best measures of activity which may serve as features in the description of organisms.

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