i i i 
METAMORPHIC CHANGES, R. PIPIENS 39 
considerable abundance. Young adults were taken only in 
small numbers, but many of the larvae completed their meta- 
morphosis in the laboratory. 
When collections were brought into the laboratory the ani- 
mals were separated into groups representing successive stages 
of development. The larvae and young adults of Rana were 
arranged in nine groups representing as many stages of de- 
velopment, which may be indicated as follows: 
Stage 1. Fore limbs concealed, hind limbs not over 5 mm. in length. 
Stage 2. Fore limbs concealed, hind limbs 10 to 15 mm. in length. 
Stage 3. Fore limbs concealed, hind limbs 30 mm. or over in length. 
Stage 4. Fore Jimbs free, tail not reduced. 
Stage 5. Tail reduced to approximately one half maximum size. 
Stage 6. Tail almost completely resorbed. 
Stage 7. Small frogs just emerged from the water. 
Stage 8. Young frogs which had just resumed feeding. 
Stage 9. Young frogs actively feeding. 
The larvae and young adults of Ambystoma were also ar- 
ranged in nine groups representing as many successive stages 
of development. The earlier stages in this series can not be 
characterized as definitely as those in the series of Rana. The 
successive stages may be indicated as follows: 
Stage 1. Larvae 9 to 10 cm. in length; weight 5 to 6 grams. 
Stage 2. Larvae 10 to 11 em. in length; weight 7 to 8 grams. 
Stage 3. Larvae of maximum size, gills not reduced. 
Stage 4. Larvae with resorption of gills and changes in coloration in- 
itiated. 
Stage 5. Larvae with gills not over half their maximum length, chang- 
es in coloration advanced. 
Stage 6. Larvae with gills almost completely resorbed. 
Stage 7. Metamorphosis apparently complete. 
Stage 8. Young adults about to resume feeding. 
Stage 9. Young adults actively feeding. 
The curves in the accompanying figures are based on the 
averages of weight determinations and measurements made on 
specimens selected from the groups representing the successive 
stages of development. Two series of groups of five specimens 
each were used in the case of each species. 
Curve A B. fig. 1, illustrates the changes in the total weight 
of the larvae of Rana pipiens as they approach and pass through 
the period of metamorphosis. It indicates a relatively rapid in- 
erease in weight until the maximum larval weight is attained, 
then an abrupt decrease from an average maximum of 6.8 to an 
