THYREOID GLANDS OF BUFO 491 
De Meuron (’86) also described the early stages in the devel- 
opment of the Anuran thyreoid glands. 
Maurer (’88) worked out the development of the thyreoid 
gland in Rana esculenta. He found the division of the median 
anlage to take place in the 13-mm. larva. At this time the 
cells were deeply pigmented, loosely arranged, and showed the 
first beginnings of vesicle formation. His account of the further 
development did not take it ap in great detail, but showed that 
by the time of metamorphosis the thyreoid was well developed, 
being composed of a large number of follicles containing colloid. 
This was very clearly illustrated in one of his beautiful figures. 
We thus see that the general development of the thyreoid has 
been pretty thoroughly worked out. It remains, however, to 
show the relation between thyreoid development and the general 
body features which become modified during metamorphosis. <A 
study of this kind involves close attention to the length of body, 
length of tail, length of limb, ete., and a comparison of these 
features with the volume of the thyreoid at various stages of 
development. In order to have any force in showing the rela- 
tion of the thyreoid gland to metamorphosis, this work must be 
done in a roughly quantitative fashion. None of the investiga- 
tors up to the present time have attacked the problem from this 
angle with one exception. Leo Adler (’14) made a few observa- 
tions upon the size of the thyreoid gland in different stages of 
Rana temporaria. His series was made up of one each, the 
length of the thyreoid gland being given in parenthesis after the 
total length dimensions of each stage. His measurements were 
as follows: 20 mm. (0.07 mm.); 23 mm. (0.09 mm.); 25 mm. 
(0.10 mm-); 28 mm. (0.16 mm.); 30 mm. (0.21 mm.); 33 mm. 
(0.82 mm.); 35 mm. (0.28 mm.); 40 mm. (0.24 mm.). He states 
that the 28-mm. tadpoles have hind legs which show a division 
into joints, but no statement is made as to their length. The 
33-mm. tadpoles have completely developed hind legs, while 
the fore legs are visible through the skin. Adler states that the 
last two tadpoles (85 mm. and 40 mm.) are abnormal in size. 
They had been hindered in metamorphosis, at first by tempera- 
ture that was too high and, later, by temperature that was too 
low. 
