Fig. 1.

Gut development in omnivorous and carnivorous anuran larvae. Ventral views of the developing gut of an omnivorous tadpole (Xenopus laevis) at Nieuwkoop and Faber (NF) stages 41 (A), 43 (D) and 46 (G) are compared to the developing guts of carnivorous Ceratophrys cranwellii and Lepidobatrachus laevis tadpoles at comparable Gosner stages (GS) 21 (B and C), 23 (E and F) and 25 (H and I). In Xenopus (A) the GD loop (arrow) is located in a proximal position along the length of the gut tube, the foregut (FG) is small relative to the midgut (MG), and the pancreas is located within the GD concavity. The GD loop is similarly positioned in Ceratophrys (B), although the pancreas is not visible early in development. In Lepidobatrachus the GD loop forms more distally, which leaves the portion of the gut tube proximal to the GD loop of more equal proportion to the prospective midgut (C). The relative positions of the developing stomach (s), liver (L) and pancreas (p) are indicated, where visible. (The pancreas remains dorsal in Lepidobatrachus and is not visible in these ventral views.) Dashed lines in G, H, and I indicate the approximate position of the embryonic midline and the left and right sides of each embryo. Images are not to scale. The cladogram (J) illustrates the relationships among Xenopus and three ceratophryine genera, including Ceratophrys and Lepidobatrachus.