This is truly one of the most disgusting things I have heard of, and in this statement I am considering the octopus whose penis-tentacle breaks off, as well as various animals in posession of what is termed a "torture phallus".

Surinam toad:

The partners rise from the floor while in amplexus and flip through the water in arcs. During each arc, the female releases 3-10 eggs, which get embedded in the skin on her back by the male's movements. After implantation the eggs sink into the skin and form pockets over a period of several days, eventually taking on the appearance of an irregular honeycomb. The larvae develop through the tadpole stage inside these pockets, eventually emerging from the mother's back as fully developed toads, though they are less than an inch long.

You really have to see the full sized image to grasp the true horror of this.