596 IODINE AND THE THYROID. Ill 



from the capillary vessels. Ten animals in Culture 5 had died, two in 

 Culture 4, none in the remainder of the cultures. 



86 hours after the first iodine was fed the larvae were again exam- 

 ined. All of the iodine-fed animals were more deeply pigmented 

 than the controls. Cultures 1 and 2 showed practically no tail 

 shrinkage, whereas this showed clearly in Cultures 3, 4, and 5. The 

 tadpoles in the stronger solutions also had well developed epithelial 

 hind limb buds. In the controls and in Cultures 1 and 2 only the 

 largest animals revealed any indications of such limb anlage. As is 

 well known, the hind limbs of the Anura develop from the epithe- 

 lium, and in the writer's experience, appear very early; but they re- 

 main mere formless buds for some time, usually until the animal has 

 attained a length of 24 or 25 mm. and sometimes even larger. The 

 limb buds then develop the two primary leg divisions and later the 

 toes differentiate. Iodine feeding causes rapid development of the 

 limb rudiments. 



March 29, 1919. 9 days from date of first feeding. Controls: average total 

 length 13.5 mm. Hind limb buds not visible without the aid of the microscope. 

 Pigmentation normal. Animals active and well nourished. 



Culture 1. — Average length 13 mm. Hind limb buds but slightly larger 

 than those of the controls, pigmentation normal. Animals well nourished. 



Culture Z. — Average length 13.5 mm. Hind limb buds large. Easily vis- 

 ible without microscope; some measured over 1 mm. in length. Pigmentation 

 dark. Slight emaciation of the body and some shrinkage of the tail-fin. It was 

 observed for the first time on this date that the tadpoles in all cultures except 

 No. 1 remain near the surface of the water. This continued throughout the ex- 

 periment, the animals descending to the bottom of the container only to obtain 

 food. 



Culture 3. — Average length 12 mm. Hind limb buds now differentiating into 

 tiny legs. Pigmentation dark. Emaciation slight. Considerable atrophy of 

 the tail-fin. Animals sluggish. 



Culture 4. — Average length 12 mm. Tiny hind legs with toes. Pigmentation 

 dark. Animals sluggish. Tail-fin atrophied. Slight emaciation. 



Culture 5. — Average length 12 mm. TinV hind legs present. Great emacia- 

 tion and tail shrinkage present. Animals darkly pigmented. Considerable 

 mortaUty. 



April 4, 1919. Controls: average length 14.5 mm. Hind limb buds just 

 visible without the microscope in animals over 15 mm. in length. 



Culture 1. — Length 14.5 mm. Identical in development with the controls 

 except for slightly larger limb buds. 



