THE AXIAL GRADIENTS IN HYDROZOA. 97 



The gradients are present, not only in each zooid of the hydroid 

 colony and in each tentacle of the hydranth, but in each axial 

 complex, e.g., a compound branch, and in the colony as a whole, 

 provided it is vigorous and growing. In general the rate and 

 amount of reduction decrease basipetally. In the medusae reduc- 

 tion is most rapid and greatest in amount in the marginal and 

 oral regions, less in other subumbrellar regions and least in the 

 exumbrellar region. Animals killed by other means before re- 

 action with permanganate show no gradient, or in some cases 

 vestiges, if newly killed. The conclusion is drawn that differences 

 in rate and amount of reduction of permanganate, as indicated 

 by the coloration, may, with proper precautions, be used as an 

 indicator of differences in fundamental physiological condition in 

 different regions of an organism. 



REFERENCES. 

 Child, C. M. 



'15 Senescence and Rejuvenescence. Chicago. 



Demonstration of the Axial Gradients by Means of Potassium Perman- 

 ganate. BIOL. BULL., XXXVI. 



The Axial Gradients in Hydrozoa. II. BIOL. BULL., XXXVII. 

 '20 Some Considerations Concerning the Nature and Origin of Physiological 



Gradients. BIOL. BULL., XXXIX. 

 Child, C. M. and L. H. Hyman. 



'19 The Axial Gradients in Hydrozoa. I. BIOL. BULL., XXXVI. 

 Cast, R. and E. Godlewski. 



'03 Die Regulationserscheinungen bei Pennaria cavolinii. Arch. f. Ent- 



wickelungsmech., XVI. 

 McClendon, J. F. 



'17 The Direct and Indirect Calorimetry of Cassiopea xamachana. Jour. Biol. 

 Chem., XXXII. 



