Most jellies release eggs and sperm into the water as they swim, which means males and females never have a chance to meet.  But one box jelly species,  Carybdea sivickisi, had evolved a more intimate attraction.  The males literally catch and reel in females using long tentacles.  Once a male has a female in his grasp, he pukes up a sperm packet to give her (jellies only have one opening, which is an all-purpose anatomy for getting things in and out). After the male pukes up this sperm packet, the lady jelly takes hold of it tenderly, and eats it.  The sperm go inside her gut, and ultimately fertilize her eggs, which she spits out a few days later.  Wanna read more, hear more, and even see more about these feisty little jellies? Check out this fantastic article by Christine Hoekenga, brought to you by the Smithsonian Institute:

http://invertebrates.si.edu/jellyfish/index.html