’ 
THYREOID GLANDS OF BUFO 501 
a sharp rise to stage VI. The body length shows a steady rise 
to stage III, when it falls off quite distinctly. This is probably 
due to the shrinkage of the intestine which brings the cloacal 
opening closer to the root of the tail than it had previously been. 
It is just at this time that the fore limbs have first appeared. 
The partly metamorphosed toads are leaving the water at stage 
V, and an appreciable loss of water from the tissues must take 
place. However, the body has really begun again to increase 
in size at stage V, and by stage VI it has exceeded the length 
attained in stage III. The tail reaches its maximum length 
in stage III, and then rapidly diminishes to the vanishing point. 
The cube root of the thyreoid gland increases more rapidly 
than does the length of the hind legs during the interval between 
the first and second stages. This is significant in that it corre- 
sponds with the results of experimental work which show that 
the hind limbs develop very slowly in tadpoles from which the 
thyreoid glands have been extirpated. It is thus seen that 
growth of the hind legs is to a very large extent dependent upon 
the growth of the thyreoid gland. 
A study of sections of the thyreoid glands shows that colloid 
begins to form at about the time when the hind limbs commence 
to develop. Compare figures 1 b, 26, and 36 and table 3. It 
increases in amount as growth continues. Measurements of 
the diameter of the larger colloid masses at different stages of 
development show a steady increase in size, very rapid in the 
early stages, as seen in table 3. In each specimen micrometer 
measurements were made of ten of the larger colloid masses. 
An average was then calculated in each case (table 3). 
The colloid masses increase in size until stage III, while in 
V there is a diminution in size. This is observed even in some 
of the metamorphosed toads, while in others the colloid masses 
have reached a size beyond that found in stage III. This table 
is clearly based upon too few observations to prove in itself 
of much value. It is of significance, however, in that it corre- 
sponds in a general way with the results of table 1. We see 
that the increase in size of the thyreoid gland corresponds with 
an increase in size of the colloid masses. It appears that this 
