SUSCEPTIBILITY IX HYDROIDS. 125 



8. The very close relation between susceptibility and physiolo- 

 gical condition is indicated by the fact that in various species 

 the characteristic gradients and regional differences in sus- 

 ceptibility often disappear or are reversed after a day or two, or 

 in some cases, after a few hours under laboratory conditions. 



9. In general the regions which are more susceptible to lethal 

 concentrations are more capable of acclimation to a certain 

 range of lower concentrations. 



REFERENCES. 

 Child, C. M. 



'14 Starvation Rejuvenescence and Acclimation in Planaria dorolocephala. 



Arch. f. Entwickelungsmech., XXXVIII. 



Senescence and Rejuvenescence. Chicago. 



Individuality in Organisms. Chicago. 

 'i6a Axial Susceptibility Gradients in Algae. Bot. Gaz., LXII. 

 'i6b Further Observations on Axial Susceptibility Gradients in Algae. BIOL. 



BULL., XXXI. 

 '17 Susceptibility Gradients in the Hairs of Certain Marine Algae. BIOL. 



BULL., XXXI. 

 'iga A Compaiative Study of Carbon Dioxide Production During Starvation in 



Planaria. Amer. Jour. Physiol., XLVIII. 

 'igb The Effect of Cyanides on Carbon dioxide Production and on Susceptibility 



to Lack of Oxygen in Planaria dorotocephala. Amer. Jour. Physiol., 



XLVIII. 



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

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



