chapter II. A number of phenomena connected with the linear rate of regeneration are illustrated and epitomised in the accompanying diagram (Fig. 40), which I have constructed from certain data given by Ellis in a paper on the relation of the amount of tail _regenerated_ to the amount _removed_, in Tadpoles. These data are summarised in the next Table. The tadpoles were all very much of a size, about 40 mm.; the average length of tail was very near to 26 mm., or 65 per cent. of the whole body-length; and in four series of experiments about 10, 20, 40 and 60 per cent. of the tail were severally removed. The amount regenerated in successive intervals of three days is shewn in our table. By plotting the actual amounts regenerated against these three-day intervals of time, we may interpolate values for the time taken to regenerate definite percentage amounts, 5 per cent., 10 per cent., etc. of the {148} [Illustration: Fig. 40. Relation between the percentage amount of tail removed, the percentage restored, and the time required for its restoration. (From M. M. Ellis’s data.)] _The Rate of Regenerative Growth in Tadpoles’ Tails._ (_After M. M. Ellis, J. Exp. Zool._ VII, _p._ 421, 1909.) Body Tail Amount Per cent. % amount regenerated in days length length removed of tail ──────────────────────────── Series† mm. mm. mm. removed 3 6 9 12 15 18 32 _O_ 39·575 25·895 3·2 12·36 13 31 44 44 44 44 44 _P_ 40·21 26·13 5·28 20·20 10 29 40 44 44 44 44 _R_ 39·86 25·70 10·4 40·50 6 20 31 40 48 48 48 _S_ 40·34 26·11 14·8 56·7 0 16 33 39 45 48 48 † Each series gives the mean of 20 experiments. amount removed; and my diagram is constructed from the four sets of values thus obtained, that is to say from the four sets of experiments which differed from one another in the amount of tail amputated. To these we have to add the general result of a fifth series of experiments, which shewed that when as much as 75 per cent. of the tail was cut off, no regeneration took place at all, but the animal presently died. In our diagram, then, each {149} curve indicates the time taken to regenerate _n_ per cent. of the amount removed. All the curves converge towards infinity, when the amount removed (as shewn by the ordinate) approaches 75 per cent.; and all of the curves start from zero, for nothing is regenerated where nothing had been removed. Each curve approximates in form to a cubic parabola. The amount regenerated varies also with the age of the tadpole and with other factors, such as temperature; in other words, for any given age, or size, of tadpole and also for various specific temperatures, a similar diagram might be constructed. ――――――――――