W. W. SWINGLE 597 



Culture 2. — Length 15 mm. Hind limbs larger than those of animals in Cul- 

 ture 1 . Pigmentation dark. Previous emaciation has disappeared. Atrophy of 

 tail-fin gradually disappearing. 



Culture 3. — Length 13 mm. Limbs larger and better developed than those 

 of animals in Cultures 1 and 2. Slight emaciation present, also tail -fin atrophy. 

 Pigmentation lighter than controls. 



Culture 4. — Length 13.5 mm. Limbs large and well developed. Some emacia- 

 tion. Tail-fin atrophied. Animals sluggish. Pigmentation dark. 



Culture 5. — Abandoned on this date. The mortality rate was too high to 

 continue the experiment. It was observed that though the death rate was high 

 during the first week of iodine feeding in quantities such as were given here, the 

 animals which survived could stand double the dosage given previously. 



April 13, 1919. Controls: Length 21 mm. Hind limbs tiny epithelial buds 

 with no differentiation into primary divisions or toes. 



Culture 1. — Length 21.5 mm. Hind limbs larger and better differentiated 

 than controls. Otherwise no difference in the animals of the two cultures. 



Culture 2. — Length 22 mm. Hind limbs fully differentiated. No emaciation. 

 No tail-fin atrophy, the atrophy apparent on previous examination had disap- 

 peared and did not occur again. Pigmentation dark. Animals remarkably 

 uniform in size, something rather unusual in a culture of frog larvae. 



Culture 3. — Length 18.5 mm. Legs fully formed and large. Pigmentation 

 lighter than controls. Slight emaciation and tail shrinkage present. Animals 

 sluggish. 



Culture 4. — Length 19.5 mm. Legs large for body, and well formed, average 

 6 mm. in length. Pigmentation dark. Tail shrinkage apparent. When exam- 

 ined under the microscope, the fore limbs were found pressing against the skin 

 of the pectoral region where later they burst through. 



It will be noted that the tadpoles were increasing rapidly in size. 

 Until this date, the controls were the largest animals, the iodine cul- 

 tures varying but slightly in this respect. It is interesting to note 

 that larv£e of a similar age, left to develop under more natural con- 

 ditions than prevail in the laboratory, had just hatched, and were 

 not over 7.5 mm. long. At the time the eggs were collected, some of 

 them were placed in a small, deep pool of clear water, plentifully 

 stocked with food, in a sheltered spot not far from the laboratory, 

 where their development was closely followed. The laboratory 

 animals averaged over 20 mm. in length before the larva3 in the pool 

 hatched. This difference in growth rate was due to the uniform heat 

 of the laboratory, and to the unseasonably chilly weather. 



