Analysis of Rate of Regeneration 401 
plete body length and tail length. It was assumed that tadpoles 
of a given species living in the same pond and varying less than 
five millimeters in length are of approximately the same age. 
Operations consisted in cutting off a selected amount of the tad- 
poles’ tails, the amount depending upon the size of the animals 
used in the series. All operations were performed with arazor 
while the tadpole lay on a block of paraffine; special care was 
taken that the line of operation be at right angles to the noto- 
chord, as occasional individuals with obliquely severed tails have 
shown an inhibition in rate during the later stages of regeneration. 
The length of the regenerating part of the tail was measured 
every third or fourth day at first; but after the greater changes 
in rate were past and additions to the new tail were being made 
very slowly, measurements were made less frequently in order 
that the differences between the last amounts recorded might be 
above the limit of error in the measurements.® 
Each tadpole was kept in a glass dish with 150 cc. of water 
and more Spirogyra than the animal would eat before a new 
supply was given to it. Water and Spirogyra were changed every 
three or four days throughout the experiments. The tadpoles of 
experiment IV were fed upon an alga of the genus, Oedogonium. 
A change of food was made in Experiment III with marked 
results. Spirogyra was chosen as a laboratory food because the 
tadpoles would subsist upon it in a healthy condition for a long 
time, and because it was a help to the conditions of the water 
instead of a source of contamination. 
The temperature under which these experiments were performed 
Was not constant, but as it varied very little from day to day 
and the greatest variation was from day to night and took place 
in the cycle of every twenty-four hours, this factor is probably 
not a source of much inaccuracy. ‘The irregularity in the gradual 
5 Measurements of body length and tail length were made with dividers and a millimeter rule while 
the animal lay upon a pane of glass over a tilted mirror. Body length is the distance from the tip of 
the snout to the tip of the tail, tail length is the distance from the angle the tail makes with the body 
at the level of the notochord to the tip of the tail. The first two measurements of the regenerated 
part of the tail were made with an ocular micrometer and are accurate to 0.04 mm. The suceeding 
measurements were made with the dividers and are accurate within 0.30 mm. 
