It is a cellular structure seen by microscope in endodermal sinus tumors(yolk sac tumors) which are the most common testicular cancer in children. They have a mesodermal core with a central capillary, all lined by flattened layers of both visceral and parietal cells. Immunofluorescent stain may show eosinophilic hyalin-like globules both inside and outside the cytoplasm that contain AFP and alpha 1-antitrypsin.