Sinclair, Bradley J., Borkent, Art & Wood, D. Monty, 2007, The male genital tract and aedeagal components of the Diptera with a discussion of their phylogenetic significance, Zoological Journal of the Linnean Society 150 (4), pp. 711-742 : 729-730

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https://doi.org/ 10.1111/j.1096-3642.2007.00314.x

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Description ( Fig. 7C View Figure 7 )

Testis: Each testis is narrow, spindle-shaped, tapered anteriorly, and organized into zones.

Epididymis: Not differentiated.

Vas deferens: The vasa deferentia are packed with mature spermatozoa, even at emergence ( Linley, 1981). The ducts extend posteriorly to near segment 9, where they bend abruptly back, become fused to the midline of the accessory gland complex, and run juxtaposed to the anterior apex of the gland. The ducts enter their respective half of the gland through a sphincter ( Linley, 1981).

Accessory gland and seminal vesicle: The accessory gland complex comprises three pairs of chambers in Ceratopogonidae , united along the midline. The most anterior chamber was referred to as the seminal vesicle by Linley (1981), and is lined with an inner layer of narrow secretory cells with spherical vacuoles containing secretions. A narrow aperture separates the seminal vesicle from the middle chamber, referred to as the glutinous gland ( Linley, 1981). The secretory cells of this chamber produce a viscid material, which forms the envelope of the spermatophore. The third chamber is not easily observed in whole mounts and is not lined with glandular cells. The entire accessory gland complex is covered in a layer of circular muscle.

Ejaculatory duct: This duct comprises two sections. In the anterior half, the ducts remain separate, whereas the ducts unite near the base of the genitalia and in this section the duct is lined with columnar glandular cells ( Linley, 1981). The ejaculatory duct is sheathed in a layer of circular muscles.

Ejaculatory apodeme, sperm pump, and aedeagus: The ejaculatory apodeme is absent and the true aedeagus is membranous. The ventral plate with its recurved tip, present in most Ceratopogonidae , is pressed into the opening of the dorsal wall of the common female spermathecal duct and may aid in stretching the opening ( Linley, 1981). The ventral plate (termed aedeagus by authors in this family) is present throughout the family, including Austroconops Wirth & Lee , an early lineage of Ceratopogonidae ( Borkent, Wirth & Dyce, 1987; Borkent & Craig, 2004).

Remarks: The male genital tract of Ceratopogonidae was first described by Pomerantzev (1932) and the method of spermatophore formation in Culicoides Latreille was thoroughly described and excellently illustrated by Linley (1981). Two packages of sperm are prepared in the long, narrow, tapering glutinous gland (middle chamber) and are pushed into paired, secreted sheaths upon exiting, which fuse medially further down the ejaculatory duct. The spermatophore is then passed to the female during copulation. As observed by Linley (1981), spermatozoa remain in the vasa deferentia until ejaculation. In the present study, spermatozoa-packed vasa deferentia were observed in freshly collected, nonmated males of Bibionidae and Thaumaleidae ( Figs 3B, D View Figure 3 , 7A View Figure 7 ), suggesting a similar process of spermatophore production as is present in Ceratopogonidae .

Remarks – features of Chironomoidea . The accessory gland complex of Chironomoidea is similar in form among all four families. The elongate second chamber with its glandular cells is similar in Ceratopogonidae , Simuliidae ( Fig. 5C View Figure 5 ; Rubtsov, 1989: fig. 10A, epsd), and Chironomidae ( Fig. 5F View Figure 5 ). Only in Thaumaleidae do the vasa deferentia enter the accessory/seminal gland subapically ( Fig. 7A View Figure 7 ).

The genital tract of the Chironomoidea is modified for the passage of a preformed spermatophore ( Wood, 1978; Wood & Borkent, 1989), the existence of which has been confirmed in the families Simuliidae , Ceratopogonidae , and Chironomidae , and presumably also the Thaumaleidae , given the configuration of the internal genital tract ( Sinclair, 1992a). The enlarged accessory gland complex is quite stout and generally easily identified in whole mount dissections, whereas the vasa deferentia and testes are often more fragile, the latter often distinctively clothed in pigment/fat granules.