502 MINNA E. JEWELL 



on the twenty-sixth day of the experiment showed that the 

 tadpoles in the first jar, which had regenerated only 2.8 per cent 

 during the twenty-two days preceding the aeration of the water, 

 had regenerated 19.8 per cent in the four days following it. The 

 tadpoles previously in higher amounts of oxygen, of course, 

 showed less difference. This experiment is of value as demon- 

 strating that the increase in the higher amounts of oxygen is 

 due to the oxygen, and not to any slight rise in temperature in 

 the successive jars, or to a decrease in the alkalinity of the water 

 as it takes up carbon dioxide produced by the successive tadpoles. 



Regeneration in low temperatures 



It has long been known that low temperatures, if not so low 

 as to produce detrimental effects, may retard or completely 

 check the development of certain animals for a considerable 

 period of time, the animal still retaining power to complete 

 normal development. The following experiment was planned to 

 test whether this might be true for regeneration. Three sets of 

 four tadpoles each were selected. The first set was kept at room 

 temperature — 19° to 21°C.; the second was kept in a water-bath 

 at 14°, and the third was kept in a refrigeration tank at 0° to 4°. 

 The first set underwent regeneration rapidly, the rate of the 

 second set was considerably retarded, the third set underwent 

 no regeneration whatever (table 8, fig. 24). When the first set 

 had completed regeneration, two from the third set were trans- 

 ferred to room temperature. The day in which they were trans- 

 ferred and several succeeding days were cool, so the temperature 

 of the water stood at 18° to 19°. For this reason, probably, the 

 regeneration of these tadpoles was slightly slower than that of 

 the controls, although the growth curves are similar. The two 

 tadpoles left at the lower temperature died without regeneration 

 at the end of forty-seven days. 



