Morphology of accessory ovaries in adult males of Perla marginata (Plecoptera: Perlidae)

Bisexual gonads in the stoneflies Perla burimeisteriana, P. pallida and Dinocras cephalotes are reported for the first time. Gross morphology and ultrastructure of the accessory ovaries of mature larvae and adult males of Perla marginata are described in detail. There are 36-58 male ovarioles situated distal to the paired testes and opening into fused termini of the lateral ducts in abdominal segments II and III. These correspond in structure to the ovarioles of adult females but are significantly smaller (maximum size of proximal oocyte 9.0 × 45 µm) and each usually contains 10-14 linearly arranged previtellogenic oocytes. Oogenesis ceases at the end of previtellogenesis or at the onset of vitellogenesis. The ooplasm contains either regularly dispersed or irregularly accumulated particles in different regions of the cell with accumulations occurring near mitochondria and Golgi complexes. Based on results of metachromatic staining, these are thought to represent either lipid droplets (most) or yolk globules. The oolemma rarely develops short microvili and few pycnotic vesicles. Development of the follicular epithelium (influencing vitellogenesis and secretory activity during choriogenesis) is abnormal. Follicular cell growth is not synchronized with that of the oocytes, and the follicular cells of the terminal (distal) oocytes show neither patency nor secretory activity. The mechanism controlling degeneration of male ovarioles and the evolutionary significance of hermaphroditic gonads in the Plecoptera are discussed.