Sentence:  <small>DOOLITTLE</small>. ... thanks to your silly joking, he leaves me a share in his Pre-digested Cheese Trust worth three thousand a year on condition that I lecture for his Wannafeller Moral Reform World League as often as they ask me ....<br /><small>HIGGINS</small>. The devil he does! Whew! [Brightening suddenly] What a <WSD>lark</WSD>! 
Meaning of the word marked with <WSD> tags:  A prank.