170 
being quite distented by a highly eosinophilic colloid matter 
(fig. 13). 
b. — In another Bufo culture a four-legged tadpole was met with 
at a juncture at which all the rest were still without legs. 
The type of the thyroid in the Control specimens appears 
from fig. 16, whereas the structure of the organ in the pre- 
cocious larva from fig. 17, displaying a considerably larger 
size together with vacuolation of the colloid matter. 
c. — In a Rana culture some early developed tadpoles were ob- 
served. The upper row of fig. B. represents three of these 
larvæ together with as many control specimens; the lower 
row exhibits the same animals a week later. As regards the 
difference in size and development of the thyroid in the two 
groups compare fig. 17 (the early developed larvæ) and 18 
(control specimen); in the former cases the follicles are larger 
and the colloid matter highly vacuolated. 
B. - Wintering Larvæ of Rana esculenta. 
In the autumn esculenta larvæ are rather commonly met with 
which have not been fully developed; such larvæ often have but 
hindlegs. Perhaps larvæ of this kind are hibernating, perhaps they 
are perishing during the winter. Kept in aquaria at 8—10° C. 
they do winter but, the metamorphosis generally will not set in till 
the spring, although the animals are fed. Fig. C. b. gives in natural 
size the look of some larvæ gathered in the month of October; 
three of them wintering in an aquarium did not change in ap- 
pearance until they were killed in April (fig. C. a.). The structures 
of their thyroids appear from pi. VI, fig. 19, viz. enlargement of the 
organ due to distension of the follicles (retention phenomenon?) 
and diminution of the epithelial cells. The thyroids of the control 
specimens, killed in October of the previous year, had the usual 
appearance characteristic of the stage of development concerned 
(fig. 20, compare fig. 24—25). 
C. Abnorraally Increased Growth (“Giant larvæ 4 ) in Rana esculenta 
In Denmark fully developed esculenta larvæ attain the size 
of 60—70 mm in length, and the recently metamorphosed frogs 
that of 25 — 30 mm (W e s e n b e r g - L u n d). As to Germany Bruno 
