A 2-year-old boy presents with an abdominal mass detected on routine examination. Imaging shows a left-sided mass that crosses the midline with stippled calcifications on CT. Urinary catecholamine metabolites (HVA and VMA) are markedly elevated. Histopathology reveals Homer-Wright rosettes. The structure marked **B** in the diagram is the site of origin of this tumor. Which of the following best describes the embryological origin and most common presentation of the tumor marked **B**?