When I visited the wondrous Icelandic Phallological Museum, I was struck at the diversity of penises found in just one country. In terms of size, the most impressive are the whale dicks. Indeed, the blue whale penis, which can range in length between 8-10 feet, is included in Smithsonian's survey of "Nine of the Weirdest Penises in the Animal Kingdom" by Corryn Wetzel.
"Blue whale penises range between eight and ten feet, with a foot-long diameter," she writes. "Each of its testes along can weigh up to 150 pounds and can ejaculate gallons of sperm in a single go."
Here's another one of the Smithsonian picks:
Sometimes one just isn't enough. Or so it seems for the echidna, a spiny egg-laying mammal, which has evolved a four-headed penis. During copulation, echidna penises operate on a part-time schedule: half the penis temporarily shuts down while the other two heads are responsible for fertilization. But those extra two heads aren't there just to show off.
Next time the echidna mates, he'll alternate which half he uses. By shutting down half of their penis at a time, male echidnas fit perfectly with the female's two-branched reproductive tract. This creature's coat of quills don't spare its genitalia, which features penile spines—a horrifying frequent trait in the animal kingdom (even humans once had them) which may increase fertilization success or trigger ovulation.