There are so many different kinds of penises. I have been thinking about a few penises. They are quite amazing.

The Tasmanian Echidna has a penis with four heads.

Echidna is the most primitive mammals still living, and displaying many archaic traits inherited from mammals’ reptile ancestor. Male echidnas ejaculate with just two heads (half of the penis) at a time. This resembles very much the way lizards and snakes ejaculate: they have a double penis (hemipenis), but only one of the two penises is used during the copulation, while the other will effectuate the next copulation/ejaculation. Marsupials (another primitive group of mammals) are now in this matter something between monotremes and placental (evolved) mammals: they do not use half of the penis for mating, but still have a double headed penis, while the echidnas have a reptilian joined hemipenis, with each part of the penis in a marsupial-like fashion.’

Leopard slug

‘Two leopard slugs in the condition to mate, crawl one after the other, the back one almost touching the front one. Both crawl towards an overhanging part of a wall or a tree branch, from where they rope down on a slime thread about 16 inches long.

Hanging freely in the air they then mate by extending their penises and entwining them. Doing so, they make a characteristic flower like structure below them, where the spermatophores are exchanged. Slugs are hermaphrodites, they are males as well as females.’

Cat penis.

‘A male cat’s penis has a band of about 120–150 backwards-pointing penile spines. Upon withdrawal of the penis, the spines rake the walls of the female’s vagina, which is a trigger for ovulation. Female cat utters a loud yowl as the male pulls out of her.’

Octopus penis.

‘The octopus penis is detachable. The male introduces penis into the gills’ cavity where it deposes the spermatophores. During the mating, the male loses its penis.’

Female ‘bed bugs have fully functioning sexual organs but male bed bugs mate by stabbing female bed bugs in the belly using their sword-like penis and ejaculating directly into the female blood stream. It’s called traumatic copulation.’

Female hyena‘s clitoris gets erected and it looks exactly like a penis.


  1. says

    My vet went into great detail about how a cats penis is spiked for forced ovulation, they always get pregnant from a coupling. It was way too much info, especially as we’d come in to organise getting kitty spayed anyway!

  2. leni says

    I probably don’t know this and have no desire to google it, but how does a spiked penis force ovulation?

    Also, what no duck penises?!

  3. briane says

    Monotremes (Echidna and platypus) are so called because they have one tube through which they crap and wee and by which they lay eggs. in that sense they are like reptiles and our cousins the birds. marsupials (pouched mammals) and placentals have two tubes through which they excrete waste, give birth and perform sex. But in no way I’s an Echidna less evolved than a human of kangaroo (or bird, lizard, nematode). This is creationist thinking. All living things are all evolved. Echidnas represent a form that exhibits similarities with lizards because of the one tube (cloaca) and egg laying, and apparent function of the penis, but extant Echidnas keep this form because it is a successful evolutionary form, not because they are less evolved or somehow primitive.

    • Nathanael says

      “Less evolved” is a phrase which could be used with technical meaning (“less derived”/”less changed from common ancestor”), but only if we actually had solid data about the underlying ancestor. Which in this case we don’t AFAIK; the fossil data isn’t informative, and the echidna may be quite highly altered from the common ancestor of all mammals.

      The coelecanth would qualify as “less evolved”, by this definition, due to its very close similarity to its ancient ancestor. Insects would be “more evolved” than centipedes. Birds would be “more evolved” compared to mammals, because they’ve changed substantially more relative to the common reptile ancestor. (By the way? I want flow-through lungs.)

      The “less evolved” may well be better adapated to any given niche. Just because we are “more evolved” than the coelecanth doesn’t mean we can swim or breathe water, which it can! A genetic pattern and body type which *doesn’t* change over a long period is in some ways truly impressive, as it must be highly adaptive to many situations.

      This isn’t what people usually mean when they say “more evolved”, of course — as you say, they are thinking in creationist or at least pre-Lamarckian terms.

  4. lpetrich says

    PZ himself has blogged on this issue: Penis evolution – Pharyngula — it’s evident that sperm-insertion organs have evolved several times.

    Another one: male sharks have claspers, extensions of their pelvic fins.

    It even evolved in plants: pollen tubes.

    Plus: more efficient way of getting sperms to eggs, resists drying out

    Minus: more mechanically complicated than external fertilization – external is ancestral

    • Nathanael says

      Plants. Learning about *all* the different families of plants blew my mind. The variety of life cycles which have evolved in plants dwarfs the number which have evolved in animals.

      Ferns — that reproductive cycle is like nothing you’ll ever see in an animal. The haploid cells (in animals sperm and eggs are haploid) each became their own creatures and grow up before producing cells which finally merge to make the new diploid fern…

      And plants are *robust*, too — I don’t know of many animals where you can take a cutting and grow a new animal. Also, animals are quite fragile to major chromosomal duplications, which most plants seem to have no problem with.

      Plants. Everyone needs to study plants. Plants are what made me really *get* evolution by natural selection. Animals provide a deeply misleading view, because in animals so many mutations cause spontaneous abortion. Plants provide a much clearer view.

      • lpetrich says

        Also in ferns, the eggs stay put and the sperms have to swim through the ground to get to the eggs — external fertilization *on land*.

        Seed plants still have alternation of generations, but most of the plant is diploid sporophyte and the haploid gametophytes are vestigial – only a few cells. I once made a list of vestigial features and it was a rather big one.

        As to the robustness of plants, also consider what mutilations they can survive.

  5. says

    Unlike platypuses and marsupials, echidnas are intelligent. Some think they may be as smart as a dog or cat. They are also long lived, having lived for longer than 50 years in captivity.

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