So worms. The picture below comes from Nature Store (I THINK).
From Hubpages this: "Each worm has four pair of setae, these are like bristles on a hairbrush and can be extended out or retracted into the worm body. The third set of setae is used in the mating process. They are used to hold the earthworms together while mating. These setae actually penetrate the mate’s body during the mating act. Once they are in position, sperm from each worm passes to the other and is collected and stored in special sacks. The process lasts 2 to 3 hours! The earthworms separate and go back to their tunnels. "
Which is also where the picture below is from.
And now on to frogs. The lad caught LOTS of frogs on vacation this summer.
All about frogs helps explain it. :)
And this video below doesn't do a great job of showing the results of mating, but it gives a general idea.