504 BENNET M. ALLEN 
ever the means by which it is accomplished, we should have to 
choose between two alternatives: either the thyreoid secretion 
does not cause the shrinkage of the tail, or it must reach a con- 
siderable volume before it is able to accomplish that result. It 
is certain that limb development and the process of disappear- 
ance of the tail follow the accumulation of colloid in the thyreoid 
glands of Bufo. 
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