A 52-year-old postmenopausal woman presents with vaginal bleeding and a 4 cm unilateral ovarian mass on imaging. Histopathology shows a sex cord-stromal tumor with characteristic "coffee-bean" grooved nuclei and multiple small rosette-like structures marked **B** in the diagram, each composed of granulosa cells arranged around a central eosinophilic basement membrane material. Immunohistochemistry is positive for inhibin and calretinin. Which of the following best describes the pathological significance of the structures marked **B**?