The sound of music from one of the class-rooms told him where he should find the Professor, and looking in at the window he saw the Crab standing beside a blackboard with notes on it waving a _bâton_, while a number of Oysters in rows were singing with their shells wide open. “Come in,” he cried, when he saw Boy, and Boy went round to the door and entered the room. “We have nearly finished,” said Professor Crab. “Perhaps you would like to hear the Molluscs sing.” “Very much indeed,” said Boy, taking a seat on one of the forms. [Illustration: 0063] The Crab counted “One, two, three,” beating time with his _bâton_, and the Oysters started singing the following song:-- “THE DEAR LITTLE OYSTER.” `"There was once a little Oyster, living underneath the sea, `Who was good as gold and, consequently, happy as could be; `She kept the house as tidy and as clean as a new’ pin, `And helped her Ma to make the beds they tuck the Oysters in.= `"We soon discovered she possessed a most uncommon voice, `And Operatic singing then became her ardent choice; `So diligently practised she her lessons and her scales, `That she quickly gained the medal given by the Prince of ```Whales.= `"Of course she now was far too good to waste her life down ```here, `So reluctantly we gave her up to grace another sphere: `She, in a barrel nicely packed, was sent to Mr. Gatti, `And under his most skilful care became an Oyster Patti."= Boy was very pleased indeed with this song, which the First Class in Molluscs sang very well, and clapped vigorously. “I’m glad you like their singing,” said the Professor, looking pleased at Boy’s approval. “That will do for to-day,” he added, dismissing the class, and the Oysters went out of the room in single file, each one making a little bow as he passed the Professor. . “Now what shall we do with ourselves for the rest of the day?” said the Crab, when they had all gone, for there is a half-holiday, you know. Would you like to go for a trip to Zum?” he asked. “Oh yes, please,” answered Boy, who remembered that that was where One-and-Nine said that they should meet again. So Professor Crab put his hat on, and after locking the class-room door set out with Boy for the Station of the Submarine Navigation Company. CHAPTER IV.--M.D. AND THE DOCTOR’S BILL. [Illustration: 9065] HEY found a boat waiting when they reached the Station, and Professor Crab having purchased the tickets they went on board the singular conveyance. They had hardly taken their seats amongst a number of respectably dressed fishes when the bell rang and they were off. Before they had proceeded far, Boy noticed a sudden rush to the great window at one side of the boat, and joining the crowd he heard some one say, “There goes the Prince of Whales.”