Anuran larvae evacuate their feces through the vent tube, which communicates with the posterior intestine and opens to the exterior. In the dextral configuration, the vent tube extends posteriorly from the body wall to the right side. The morphology and microanatomy of the dextral vent tube configuration were studied in various species classified into three categories: (1) marginal external tube, (2) nonmarginal external tube, and (3) without external vent tube, but with an external aperture in the posterior wall of the body. These dextral configurations were compared to medial vent tube configurations in Orton larval types 2, 3, and 4. Although vent tubes show greater morphological diversity in the dextral than in the medial condition, the histological organization in all cases is based on the same tissues (dermis and epidermis), and, thus, the medial and dextral configurations are fundamentally similar. Part of the cloaca located in the pleuroperitoneal cavity has a region covered by ciliated epithelium, which suggests that it is derived from the proctodeum. Cilia remain in the cloaca, until at least Gosner Stage 34. The rectus abdominis muscle fibers are orientated in a different direction relative to the cloaca in tadpoles with different ecotypes.
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Vol. 60 • No. 2