Embryonic and larval hemoglobins during the early development of the bullfrog, Rana catesbeiana.

The main hemoglobin (Hb) found in Shumway (embryonic) stage 25 bullfrogs is that which we have designated Td-4. The other major tadpole Hbs (Td-1, 2, and 3) predominate during Taylor and Kollros (larval) stages I-XVIII. We propose that Td-4 is an embryonic Hb, whereas Td-1, 2, and 3 are larval (fetal-like) Hbs. Embryonic Hb Td-4 continues to be synthesized during the larval stages. During the larval period, the average peripheral blood Hb profile changes very little with morphological stage or general growth. However, there is great heterogeneity in the embryonic:larval Hb ratio among individual tadpoles of a given stage or weight, apparently due to differential Hb and red cell production by the two active erythropoietic sites, mesonephric kidneys (Td-4), and liver (Td-1, 2, 3).