THYREOID GLANDS OF BUFO 499 
opment in each group. With the material at hand it was impos- 
sible to judge the age of the specimens. This would be quite an 
unsatisfactory method of seriating material, even in laboratory- 
reared specimens, because of the large amount of individual 
variation in the rate of growth of tadpoles. ‘Temperature con- 
ditions play a large part in determining the rate of growth. Any 
attempt to regulate this factor would probably entail abnormal 
Relation between thyreoid growth and metamorphosis in Bufo lentiginosus 
Stage I II Ta IV Ve Wat 
Hind leg length Curves mark ratio of dimen- 
veoreeeee Tail length sions at various stages to di- 
=——— Body length mensions of structure at com- 
mae Thyreoid volume pletion of metamorphosis. 
Fig. A Curves to show the relative rate of growth of the total length, body 
length, and hind-limb length as compared with the growth of the thyreoid gland 
during metamorphosis in Bufo lentiginosis. 
conditions that would modify growth in other ways. It is 
difficult, at best, to bring about normal development of tadpoles 
under laboratory conditions. For these reasons it was decided 
to use specimens caught under natural conditions and seriated 
as indicated above. 
JOURNAL OF MORPHOLOGY, VOL. 32, NO. 3 
