502 BENNET M. ALLEN 
growth of the glands is, in fact, brought about by the accumula- 
tion of colloid substance. In the first stages of colloid formation 
there were only from five to ten colloid masses. These soon be- 
came very numerous, as shown in figures 1 b, 2b, and 3b. No 
satisfactory conclusions were drawn from a study of the epithe- 
lium of the follicles, although it is quite possible that important 
points might be gained by an application of special methods 
of technique upon the problem of the manner in which they 
elaborate the thyreoid secretion. 
TABLE 3 
Table of measurements of colloid masses in the thyreoid gland of Bufo lentiginosus 
AVERAGE COLLOID 
TOTAL LENGTH BODY LENGTH HIND-LEG LENGTH DIAMETER 
é 
mm, mm. mm. mm, 
8.4 3.4 
8.4 Bere No colloid present 
8.9 3.8 
9.1 4.3 
11.4 5.5 0.245 0.0122 
14.6 6.9 0.357 0.0138 
15g 8.4 0.0147 
20.8 9.5 0.0284 
20.8 10.6 2.805 0.0258 
23.6 11.8 4.884 0.0559 
24.8 11.4 6.270 0.0603 
13-4 10.1 7.623 0.0499 
12.0 12.0 10.164 0.0478 
12.3 12.3 11.055 0.0672 
SUMMARY AND CONCLUSIONS 
The accumulation of colloid material in the thyreoid glands 
of toad tadpoles begins just as the hind limb buds appear. The 
colloid masses continue to increase in size and number until 
the fore hmbs break through the skin. This accumulation of 
colloid material is accompanied by a marked increase in the size 
of the thyreoid glands, which appears in the main to be a direct 
result of it. . 
A series of observations upon the effect of thyreoid extirpation 
in Rana and Bufo upon limb development have shown that the 
