What you need:
If thawing the slug leave in tube or bag in warm water bath.
Before Dissection can begin the sticky slime should be delt with. The slug can be difficult to work with otherwise. The outer mucus can be removed by running the dull side of a scalpel against the body and pulling cliumps with forceps as seen pictured below.
The first cut will be separating part of mantle from the main body. This cut will be just below the pneumostome (the breathing hole on the side of the mantle). It is important to take great caution not to cut into the intestine/colon. If the intestine are cut then everything gets contaminated with the intestinal bacteria. The anus is located just behind the pneumostone so start the first incision just in front of the pneumostome and stopping just under the pneumostome.
Observe this first cut and notice where the colon is; it should be filled with dark fecal matter. Try cutting with the scalpel against the inside of the mantle to avoid tearing the anus or cutting the colon.
Once a little more than half of the mantle is separated from the main body pull back the mantle. The mantle flap will be pinned down.
Next The foot flesh will be separated from the main body. Try to keep the scalpel along the inside of the foot to avoid cutting the intestine and other organs. The forceps can be used to pull up the skirt and give plenty of room for scalpel to cut.
It is a good idea to start the separation from the tail end of the slug because it is less crammed with internal organs.
From here you can keep an eye on the internal organs to avoid accidental cuts and maybe even hold them back with the forceps to give more room for the scalpel. keep cutting downward until you are close to the anus. At this point decide how you are going to cut the last of the right half of the skirt.
Now that you have separated most of the mantle and foot from the main body all these flaps of flesh can be pulled apart and pinned down. Be careful pulling apart the organs at this step many or wrapped up in connective tissue. The intestine are wrapped around the digestive glad throughout the body and will stay stuck together until near the end of the dissection.