I this quote from Drs. Kelly and Orbach in this Discover Magazine article really sums harbor porpoises up well:

“An erect harbor porpoise penis goes up to its chin — or, where its chin would be, if it were not a marine mammal,” Kelly said. And their vaginas are the most complex of the four, with “a whole bunch of spiraling folds,” Orbach explained, “which just keep twisting around … a little bit like a corkscrew.”

But these journal articles are also really interesting reads (and they’re both open access, I believe).

Orbach, D.N., Kelly, D.A., Solano, M. and Brennan, P.L., 2017. Genital interactions during simulated copulation among marine mammals. Proceedings of the Royal Society B: Biological Sciences, 284(1864), p.20171265.

Orbach, D.N., Marshall, C.D., Mesnick, S.L. and Würsig, B., 2017. Patterns of cetacean vaginal folds yield insights into functionality. PloS One, 12(3), p.e0175037.

This is a series of little illustrated factoids about animal reproduction, posted daily. I’d love to hear your suggestions/ feedback. I also post these on my insta.