414 Marion L. Durbin 
known thickness. Every fiftieth section was drawn with a cam- 
era lucida, and the area of each drawing determined with a plan- 
imeter. The table gives the volumes in cubic millimeters, as 
computed from these section and drawings. 
An examination of these data make it evident that the maxi- 
mum rate of increase in volume is near the tenth day; after this 
time the rate is much lower, but the irregularity of the data makes 
it impossible to say anything definite about the decrease in rate. 
DISCUSSION 
A glance at the data is sufficient to reveal a general similarity 
between the changes in the rate of regeneration of the tadpole’s 
tail and the changes in the rate of growth throughout the life 
of an animal. The rate of regeneration and of ordinary growth 
decreases from a maximum, attained soon after the process be- 
gins. ‘The decrease is rapid at first, and then becomes gradually 
slower and slower. Minot (’08) conducted an elaborate series 
of experiments upon the rate of growth in rabbits, guinea-pigs 
and man, and expresses his results graphically by constructing 
curves showing the per cent of increment per day, throughout 
the life of the animal. ‘These curves when based upon the rate 
changes, either from the time the egg is fertilized, or from the 
time the animal is born, show that the raté of growth undergoes 
four different kinds of change, which corresponds in general with 
the four intervals of change in the rate of regeneration. Minot 
does not emphasize the first two changes in the rate of growth, 
and they have no place in his discussion of the subject. In his 
study of the rate of growth, beginning with the fertilization of the 
egg, he remarks upon the fact that during the cleavage period 
there is no increase in weight. Also he makes frequent reference 
to the fact that it is sometime after birth, three to eight days, 
before the rate is at its maximum. In either case the initial inter- 
val of low rate is relatively shorter in the growth curve than in the 
curve of rate of regeneration. ‘The second interval in the rate 
of growth is probably very short. It is combined with the first 
in all the figures given by Minot. It is in the regions of decline 
