Are you Curious about Penis-fencing Flatworms?

I fell for this one 30 years ago, when it was called "The Biological Basis of
Human Sexuality." We knew they wouldn’t be showing stag films
in a Harvard biology course, unless they were about the horned rather
than the horny variety.  However, by the third week we would have
been happy with stags, or any mammals for that matter. It turned
out the biological basis of the title rarely involved creatures more
complex than insects, and was largely confinded to microscopic multicelled
organisms and how they procreate. The professor seemed to take a malicious
delight in our obvious disappointment and piled on the zygotes and mitochondriae.
Classic bait and switch.

It looks like this year’s version hasn’t changed much, although it seems to have a little more truth in advertising, and a blog.
  Or maybe professors these days are just a little slicker with the
old B & S.  Anyway here are some teasers from the class Blog
for Biology H95 fi:

Are you curious about penis-fencing flatworms . . . voracious
female spiders who
demand
their
mates offer
themselves
as
a
nuptial meal
. .
. sneaker male fish who gain a reproductive advantage by virtue of
stealth and oversized testes . . . chaining behaviors in hermaphroditic
sea slugs
. . . male birds who are virtually flightless by virtue of their
sexual ornaments . . . female fruit flies who have evolved defenses to
counteract
the toxic seminal fluids their mates provide? Then maybe you’ve been
looking for Biology 95hfi: Sex: Everything You Ever Wanted to Know
About It and Then Some

from the Sex Tutorial Weblog