THYREOID GLANDS OF BUFO 503 
limb buds appear simultaneously in both the control and oper- 
ated tadpoles. Soon after their appearance the limb buds of 
the thyreoidless tadpoles lag far behind those of the normal 
controls. They finally grow to an appreciable degree in spite 
of the absence of the thyreoid gland, but never so fast nor to 
any degree approaching the length relative to body length at- 
tained in the normal controls. These observations will be ex- 
tended during the coming season and published later. It is 
clear, however, that the effects of thyreoid removal first become 
evident in Bufo at the period when colloid normally begins to 
accumulate. A comparative study along this line would give 
some valuable hints upon the real significance of colloid secretion 
and accumulation. 
We have next to consider the apparently paradoxical fact 
that there is a cessation in growth and an actual diminution in 
the size of the thyreoid glands and of the colloid masses at the 
very time when the process of metamorphosis is most active 
(stage V). This might in part be explained as the result of a 
partial drying process due to the emergence of the tadpoles from 
the water, were it not for the fact that they do not emerge upon 
the land until stage V. The reduction in size is thus under way 
before this factor could prove effective. It is much more prob- 
able that this diminution may be due to the absorption of an 
unusually large amount of stored colloid at this time when it 
would prove most effective. It is quite conceivable that sub- 
stances might be elaborated in the blood that would enable it 
to more readily dissolve the colloid and that its solvent power 
might decrease again after metamorphosis has been completed. 
Of course this is pure conjecture, but it is put forth in the hope 
that it may: prove suggestive. 
The development of the tail presents an interesting problem. 
It steadily increases in size until stage III, shows a slight diminu- 
tion to stage IV, and then quickly disappears. It might be 
assumed that a certain amount of thyreoid secretion must be 
elaborated before the absorption of the tail can be accomplished, 
or, if our assumption of a more solvent condition of the blood 
should prove true, it might serve to explain this point. What- 
