A) Shiner perch (Cymatogaster aggregatei) paired intromittent
organs are housed within a surrounding sheath on the anterior portion of the anal fin and a single fleshy genital papilla located ventrally on the abdomen anterior to the anal fin (left side of body shown in figure); B) Walleye surfperch (Hyperprosopon argenteum) single genital papilla located ventrally on the abdomen anterior to the anal fin.
"We refer to these genital spines as intromittent
because they insert [them] into female external genitalia during copulation, and not because they insert into the reproductive tract," said the authors.
If these flies lack an intromittent
organ, how is sperm transferred during copulation?
Copulation "plugs" made by a hardening of seminal fluids in the female reproductive tract or by the tip of the male's intromittent
organ breaking off, have been reported for several spider species Phidippus johnsoni Peckham & Peckham 1983 (Jackson 1980), Agelena limbata Thorell 1897 (Matsumoto 1993; Yoward & Oxford 1996; Schneider et al.
Males were designated sexually mature according to the criteria of Van Engel (1990): the second pleopods lay within the first pleopods (intromittent
organs); the penes were inserted into the second pleopods; and the abdomen easily pulled away from the sternum.
For example, larger males mature much later and have disproportionately longer and higher dorsal fins and disproportionately smaller gonopodia (the modified anal fin that serves as an intromittent
organ) and testes.
In widow spiders (Latrodectus), the tip of one or both of the male's intromittent
organs (emboli) often breaks-off during copulation to be left inside the female's genitalia (Levi 1959; Bhatnagar & Rempel 1962; Wiehle 1967; Kaston 1970; Berendonck & Greven 2002; Segoli et al.
Of the male characters, the genital sac and male intromittent
organs are lost most often.
External female genitalia were examined, including shape and size of the epigynal guide pocket, intromittent
orifices, spermathecae and spermathecal apophyses.