ENVIRONMENT AND REGENERATION 505 



3. Unfavorable hydrogen ion concentrations inhibit regener- 

 ation directly by affecting the regenerating tissue, and indirectly 

 by affecting the tadpole as a whole. The direct effect is relatively 

 independent of the size of the tadpole, the indirect effect is greater 

 in smaller tadpoles (p. 498). 



4. In water of low oxygen content both the rate of regeneration 

 and the total amount regenerated are dependent upon the amount 

 of oxygen present (table 7; figs. 21, 22, and 23). 



5. Both the rate of regeneration and the total amount regener- 

 ated decrease with a decrease in temperature (table 8; fig. 24). 



6. The phenomena of differentiation in regenerating tissues, 

 as indicated by the appearance of pigmentation, are not retarded 

 to the same extent by unfavorable hydrogen ion concentrations, 

 insufficient oxygen, or low temperatures as are the phenomena 

 of growth or elongation. This, it is suggested, may explain the 

 decrease in the total amount ultimately regenerated due to the 

 unfavorable environmental factors studied (p. 504). 



7. Carbon-dioxide production is increased by bases and de- 

 creased by acids. A high rate of carbon-dioxide production, 

 when induced by a basic medium, is not correlated with a high 

 rate of regeneration (table 3; figs. 7, 8, 9, 10, 11, and 12). 



8. Both the relative decrease of carbon-dioxide production in 

 acids and the relative increase of carbon-dioxide production in 

 bases increase as the size of the tadpole decreases (p. 497). 



9. Although the extent to which any environmental factor 

 may affect a given life process may vary with size, age, etc. 

 (p. 497), and although different processes in the same individual 

 may be affected to a different extent by the same environmental 

 factor (p. 504), it is suggested that unsuitable hydrogen ion con- 

 centrations, insufficient oxygen, low temperatures, and toxic 

 substances affect development, regeneration, oxygen metabolism, 

 and duration of life in the same way and according to the same 

 laws. 



This work was done in the Zoological Laboratory of the Uni- 

 versity of Illinois, under the direction of Dr. V. E. Shelford, to 

 whom the writer is indebted for many courtesies and valuable 



