Which animal species mate ventrally, but upside down ?

In Xanth, any species can mate with any other it wants to, and some of the offspring are fine people.

Early on, our species mated more often but over the eons, that interval has changed to a cycle of a millennia or so.

Some species mate opportunistically while foraging in light gaps.

Some species of birds mate frequently, others only once.

He had a rough notion how this species mated, but this hardly mattered.

'But I thought different species could not mate unless they were closely related,' Aquilon said.

The species are mating in the spring, during which time, both sexes turn green, but the males remain darker.

The fact that humans have 46 and chimps have 48 makes it so our species cannot mate together anymore.

Some people will have a hard time accepting that two species can mate.