The backwards-facing priapium has both reproductive and digestive functions, with the opening of the anus set in one end and a genital pore set in the other. It has two conspicuous externalised bones -- the curved toxactinium, which juts out from under the mouth, runs down the throat and connects under the skin to the rest of the priapium structure, and the short, serrated ctenactinium, which looks like a tiny, toothy lower jaw bone. Scientists have suggested that the reason this bone is lined with seven hook-like serrae is for the purpose of grasping onto a female's head during copulation. Because her oviduct is convenienrly located at her throat.
Besides the clasping component of this organ, there is also what's known as the papillary component, which is responsible for transferring sperm bundles into the female. Once the female's oviduct is filled with sperm, she is able to lay eggs that were internally fertilised. [...] No one knows exactly why P. cuulong and priapiumfish evolved to have their genitals on their heads, but one thing's for sure, she said, "There's not much going on at the back of these fish".
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