I found this inside a hen I culled, it felt like a jelly filled sac but when I cut it open clear fluid that looked just like water and had no smell came out. it looks like there is a tube leading from it to the vent but there didn't seem to be an opening from the sac containing the water to the tube. If I didn't know any better I'd say it was a chicken bladder! But they don't have bladders and in any case there was no ureters from the kidneys. For orientation on the pic the vent is near my fingers, breast up at the top.