You got it. A nymph is the bug's life when they are crawling around rocks and living in the water. The nymphs won't always have a bead for a head, some do some don't.
The bushier dry fies helps it stay on top of the water, when you spray it. Here are some pics.
http://www.google.ca/imgres?imgurl=http://s4f04ccd39158b.img.gostorego.com/802754/cdn/media/s4/f0/4c/cd/39/15/8b/DRY_20FLIESmay_flies.jpg&imgrefurl=http://www.iwantdirect.com/uk-fly-fishing-tips/dry-flies/&h=1067&w=1600&sz=207&tbnid=cBeUSrqS4A-_wM:&tbnh=77&tbnw=116&zoom=1&usg=__DJ_DADPM4KoXc3kWbwaNJgogbNo=&docid=HUUALPU-VTm8bM&hl=en&sa=X&ei=6KimUM_mAoikyQG_jICoBw&ved=0CEUQ9QEwAQ&dur=1171
They need to be stored in a thicker box, obviously.
Wet flies and nymphs can have lead tied in the body to make it sink faster or stay near the bottom. Dry flies tend to have thin wire hooks so they are lighter.