Pelvic amplexus in Xenopus (Pipidae: Anura)

The South African clawed frog (Xenopus laevis) was formerly widely used in a pregnancy test, where females frogs were injected with an extract of urine from the women to be tested. The presence a characteristic pregnancy hormone (gonadotropin) induces ovulation in female frogs. Injection of male frogs with a purified hormone extract  also brings them into breeding condition within a few hours: the male grasps the female in front of her hind legs (pelvic amplexus) and releases sperm, which fertilizes the eggs (black dots) as they are shed. By this means, it is possible to test the potential for hybridization between the twenty of so species of Xenopus.