Dissolve gelatin in water. Let stand 5 minutes. Beat egg yolks and sugar until light and fluffy. Add lemon juice and lemon rind. Blend carefully. Melt gelatin with water over low heat. Add to egg mixture, stirring well. Whip cream. Fold cream into egg mixture. Beat egg whites until stiff peaks form. Fold into egg mixture. Pour mousse into 4 serving bowls. Chill in refrigerator for about 2 ½ hours. Garnish mousse with lemon peel and a dollop of whipping cream, if desired.