I have found that after teaching dovetail executions when angles are correctly fitting it usually comes to the corners and fitting corners can be tricky.Trash build up in the corners can cause a dovetail to fail. All surfaces have to fit but leave room for glue.
Spiders are metal brackets spanning between all legs and the center post to keep the legs from spreading. Well fit dovetails should hold the base and legs together without spiders but once you have your gold bullion set in place you will need all the stability (spiders) you can get!
Tim, The table base you asked about was Admiral Byrd's dining table base from Rosemont (Berryville (Battletown), Virginia). Restored and delivered with minimal damage exposed to an original family member. The extension for this table were an art of there own and still working with very little needed more than wax and a bit of glue.
I remember this table as a youngster extending out forever. I always thought air craft carrier and if I was flying a plane over rough water this is what I would want to land on. Not that I ever did that. It was just a thought when you were 10 -12 years old.
Looking at the sections, and the amount of, I wood figure 20-22 inches per leaf with 5 extensions on both sides.
We had this table after a bad move to repair a small break.
This table, as with 97 percent of all period furniture our attention should be towards internal construction, is an engineering feat of it's own. It only has four remaining leaves today.
Very little of the repairs needed any added pieces. The arched supports had double tennons and a few splinters were missing between the mortises. I do love puzzles. The base had already seen significant veneer restoration. It was sad to see but was gratifying to be part of the restoration of my past. I hope that time respects my restoration.