Animal Genital Diversity

In several insects and spiders, spermatophores function as nuptial gifts containing nutrition that can support the egg-producing partner. Barnacles can have penises many times their own body length, making them proportionally among the largest in nature. The duck female reproductive tract includes counter-oriented corkscrew structure and cul-de-sacs that can trap sperm, showing female counter-adaptations to the male penis. Some hermaphroditic slugs can chew off a penis when mating partners become stuck, a process called apophallation. Some hypodermic penises are needle-like structures that do not target the genital tract but inject sperm through any part of the body wall. The male paper nautilus detaches a sperm-loaded arm onto the female and escapes, reducing his risk of being eaten. Spiders use pedipalps, which serve both sensory and sperm-transfer functions, for reproduction. A broken-off genital part in some invertebrates can act as a mating plug, blocking subsequent males from mating with the same partner. Duck penises are corkscrew-shaped and emerge ballistically during copulation.