Nuptial pad

A nuptial pad (also known as thumb pad, or nuptial excrescence[1]) is a secondary sex characteristic present on some mature male frogs and salamanders.

[2][3][4][5] Triggered by androgen hormones, this breeding gland (a type of mucous gland) appears as a spiked epithelial swelling on the forearm and prepollex that aids with grip, which is used primarily by males to grasp (or clasp) females during amplexus.

[6] Austrian biologist Paul Kammerer experimented on midwife toads' nuptial pads.

[7] He used the offspring's apparent enlargening from generation-to-generation as evidence of Lamarckian evolution.

[8] Many amphibian species manifest nuptial pads for use in amplexus, an example being the rough-skinned newt, Taricha granulosa.