<i>Ntl</i> mutant sperm are immotile and are not transferred into seminal vesicles.

<p>Panels A, B, E, and F: Phase contrast images of testes from <i>Ntl⁺</i> (A, E) and <i>Ntl^-</i> (B, F) males. The major phenotypic feature of the mutants is the accumulation of coiled cysts at the base of the testis (asterisks), and the empty/shrunken state of the seminal vesicle (arrows). Panels, C, D, G, and H: <i>don juan-</i>GFP fluorescence images corresponding to phase images immediately above them, showing the disposition of elongated cysts and mature sperm in the testis and seminal vesicle. Note the complete absence of fluorescence from the seminal vesicle of <i>Ntl/Ntl</i> mutants (arrows) compared to the accumulated fluorescence in wild type seminal vesicles (arrowheads), and accumulation of coiled cysts in the base of the mutant testes (asterisks). In panels A and C, the letter M demotes dense masses of mature motile sperm which is not seen in the mutants. Left hand panels: wild type (<i>Ntl/+</i>); right hand panels: <i>Ntl</i>^129A/<i>Ntl</i>^129A mutants. Bars, 20 µm.