There were some very large turtles in the tank, swimming by moving their broad flippers. Sometimes they would swim about close to the white tiled bottom of the tank, but the water was clear, so they could be seen easily. Again the turtles would rise to the top, so that their big, hard shells were out of water, like a raft which the boys build to play with when the city's vacant lots or country meadows are flooded in the Spring.
In one end of the tank was a big turtle--the largest of all--swimming by himself, and overhead, hung by a wire from the room, was a stuffed one, larger yet. This, so a sign near it said, was a "leather-back turtle," and when alive had weighed eight hundred and fifty pounds.
"Whew!" whistled Bert, looking at the big, stuffed fellow. "He could swim around with two or three boys on _his_ back."
"I'd like to have had a ride on him," cried Freddie. "But this one is pretty big, too!" and he pointed down at the large swimming turtle, which, just then, stuck his head up out of the water. He seemed to be nearly a yard long and almost as broad.
"Oh!" screamed Flossie, as she saw the big turtle so close to her. "Can he get out of the water, Daddy?"
"I can't see him very good," said Freddie, and he gave a little jump up from the foot-rail on which he was standing.
Freddie must have jumped up harder and farther than he had any idea of, for before Bert, who was standing near his little brother, could put out a hand to hold him, the flaxen-haired twin had fairly dived over the rail, and down into the tank he fell with a great splash.
No, not such a great splash, either, for Freddie did not fall directly into the water. Instead, only his two fat legs and feet went in, for the small boy landed, sitting right up on the broad back of the big turtle! Right down on the turtle's back fell Freddie Bobbsey!
There was a scream from Nan, another from Flossie, and a sort of grunt of surprise from Bert, as they saw Freddie disappear over the railing of the tank, and come into view a second later on the back of the turtle, which was as much surprised as, probably, the little boy himself.
"Here, Freddie! What are you doing down there?" asked Mr. Bobbsey, before he thought what he was saying. He and his wife had so often to ask what Flossie or Freddie were doing, as the smaller twins were so often in mischief, that the father did it this time.