Vasa deferentia and associated structures of the male Panorpodes kuandianensis (Mecoptera: Panorpodidae).

The male reproductive system may provide significant evidence for the taxonomic and phylogenetic analyses of insects. However, current knowledge of the male reproductive system in Mecoptera is mainly concentrated on the external genitalia, and is rarely involved in the internal reproductive system. Here, we investigated the morphology and the fine structure of the vasa deferentia and associated structures of the male reproductive system of Panorpodes kuandianensis Zhong et al., 2011 (Panorpodidae) using light, scanning, and transmission electron microscopy. The male reproductive system of P. kuandianensis consists of a pair of symmetrical testes with three tubular testicular follicles, two epididymides, two distinctly partitioned vasa deferentia, a pair of mesadenia, one ejaculatory sac, and the external genitalia. A pair of expanded seminal vesicles are modified from the median part of the vasa deferentia, and evolve into secretory organs. The seminal vesicles have elongated cylindrical epithelial cells, which contain abundant secretory materials in the cytoplasm and form a small central lumen, likely serving a secretory function rather than provisionally storing sperm as in most other insects. Alternatively, the sperm are stored temporarily in the epididymis, the greatly coiled portion of the vasa deferentia. The morphology of the male reproductive system supports the close relationships of Panorpidae and Panorpodidae.