Step 1In a medium bowl, stir together the mayonnaise, chives, tarragon, chervil and lemon juice until light and creamy. Season with salt and pepper to taste. Set aside.
Step 2Pick over the watercress, discarding the tough stems and keeping the leaves and tender stems as intact as possible.
Step 3Place the crabmeat in a medium bowl and gently stir in just enough mayonnaise that the crab is lightly coated and delicately bound. This will probably take about half of the mayonnaise.
Step 4Combine the endive and watercress in a salad bowl. Add the remaining mayonnaise and toss to dress lightly.
Step 5Divide the endive and watercress among 6 well-chilled plates, arranging the greens in the centers in neat mounds. Arrange the crabmeat over the greens. Squeeze a few drops of lemon juice over the crab and serve immediately. Garnish with additional lemon wedges.