part of develops from ends during starts during venous endothelium left lymph heart XAO:0000372 The leftmost of the two lymph hearts, pulsatile organs that are present in lower vertebrates and function to propel lymph into the venous system. Two bilaterally symmetrical lymph hearts can be seen adjacent to the somites 3 and 4 by NF stage 40, and can be seen beating by NF stage 43. xenopus_anatomy death cavitated compound organ lymphatic system NF stage 32