440 Max Mapes Ellis 
and they still remained as active as those kept at the higher tem- 
peratures, at which regeneration took place. It is also known, that 
tadpoles will live at evena lower temperature than 47° F.; they have 
been collected by the writer from ponds in which there was floating 
ice, and the water of which was certainly not above 38°F. Taking 
the temperatures as observed, however (57 to 96° F.), regenera- 
tion is absent, present and prohibited by death, in a gamut of 
forty degrees. ‘The absolute thermal limits of regeneration, as 
found in these experiments, were 82° and 66° F., a range of but 
16°. Between these limits the data collected show the amount 
regenerated to vary in the same direction with the temperature. 
This is particularly apparent in Experiments 2 and 3, but may be 
shown to be the rule for all of the experiments by cross-comparison. 
Two conclusions were drawn from the data collected concerning 
the relation of temperature to the amount regenerated: 
1 There is a minimum temperature, below which tadpoles live’ 
but do not regenerate the tail. It lies between 57° and 66° F. for 
tadpoles, body length 37-42 mm. 
2 Between 66° and 84° F., the amount of regeneration varies 
in the same direction as the temperature. 
Level of Injury 
Spallanzani in 1769 made the following interesting statement 
concerning the relation of the level of injury to the amount regener- 
ated, in the tadpole tail. He says: “If the whole tail, or very near 
the whole tail, be cut off, the tadpoles go to the bottom of the 
water and there lie down and perish. But if a lesser part be taken 
off, not one of them dies; and all without exception, recover what 
they lost. . . . . Nature observes the following laws in 
the growth of these reproductions. ‘They are more considerable, 
when a great part is taken off; not so large after a lesser section’ 
and least of all when a very small bit has been cut off. The 
greatest length seems however, rather to take place, when the 
tail is divided in the middle, than when the section is higher.” 
The relations of the level of injury to the regeneration were found 
to be precisely those pointed out in the observations of Spallanzani. 
First as regards the level from which the removal of the tail pro- 
