CIRCULATORY PATTERN AND STRUCTURE IN THE TAIL AND TAIL FINS OF XENOPUS-LAEVIS TADPOLES

This investigation was initiated with the intent to study capillary sp routing in the tadpole tail fin microcirculation of the African clawed frog, Xenopus laevis, using a combination of intravital video recordi ngs and electron microscopy. The tadpoles were observed daily for peri ods up to one hour during one to two weeks. The capillary sprouts orig inated mostly from postcapillary venules, and within 24-48 h merged wi th other capillary sprouts, subsequently establishing a capillary loop with blood flow. As the circulatory patterns developed further, capil lary regressions also occurred. As the electron microscope analyses of the capillary sprouts progressed, it became obvious that a thorough e lectron microscope study of the blood vessels of the tadpoles was requ ired in order to explore structural characteristics of arterial and ve nous blood vessels. Thus, this article deals primarily with the genera l organization of the tadpole tail circulation, and the ultrastructura l characteristics of the vascular walls. A subsequent article will dea l with the role of endothelial cells, fibroblasts and pericytes in the processes of capillary sprouting and regression, based on intravital recordings and electron microscope analyses.