500 BENNET M. ALLEN 
The growth of the hind limbs was arbitrarily represented by 
a straight line inclined at an angle of 45°. Upon this were marked 
off intervals indicating the average length of the hind limbs at 
the given stage as compared with the average length at the 
stage of metamorphosis (stage VI). From each of these points 
a perpendicular was dropped to the base line. These perpendicu- 
lars then served to indicate the six stages chosen. Their distance 
from each other serving to indicate the probable time intervals 
between the different stages upon the assumption that the growth 
of the hind limbs takes place at a uniform rate. Points es- 
tablished upon these verticals serve to indicate the average 
dimensions of various features at each of the six stages studied, 
the height from the base line showing the proportion that the 
dimensions of any given feature of that stage bear to its dimen- 
sions at the time of metamorphosis—stage VI—maximum de- 
velopment in the case of tail length. Curves were constructed by 
joining these points, thus giving the proportional rate of growth 
of each feature. The cube root of the volume of the thyroid 
gland was employed because it would represent one dimension 
of a cubical figure whose volume would roughly represent the 
volume of the thyreoid gland. This appeared to be the best 
criterion of comparison, because each of the other features was 
represented by a one-dimension value as body length, tail length, 
and hind leg length. In reality all of these features have length, 
breadth, and thickness. Any influence that the thyreoid gland 
would exert upon their growth would be the influence of one 
solid body upon another. The length of the thyreoid gland 
could not be taken as a criterion of comparison, because it in- 
creases little during the stages, while the volume of the gland 
increases greatly, owing to growth in thickness. Thus it seems 
that the fairest basis of comparison would be to compare the 
cube root of the volume of the thyreoid with the length dimen- 
sions of the body, tail, and hind limb. 
It is noted that the cube root of the thyreoid volume shows 
a marked rise from stage I to stage II, from which the rise con- 
tinues strongly to stage III, then more strongly to stage IV. 
There is a slight fall in the curve from stage IV to stage V, with 
