"Let us go down," said Glenarvan; "the thunder will soon burst over us."

On returning to the bottom of the tree, they found themselves, to their great surprise, in a sort of dim twilight, produced by myriads of luminous specks which appeared buzzing confusedly over the surface of the water.

"It is phosphorescence, I suppose," said Glenarvan.

"No, but phosphorescent insects, positive glow-worms, living diamonds, which the ladies of Buenos Ayres convert into magnificent ornaments."

"What!" exclaimed Robert, "those sparks flying about are insects!"

"Yes, my boy."

Robert caught one in his hand, and found Paganel was right. It was a kind of large drone, an inch long, and the Indians call it "tuco-tuco." This curious specimen of the COLEOPTERA sheds its radiance from two spots in the front of its breast-plate, and the light is sufficient to read by. Holding his watch close to the insect, Paganel saw distinctly that the time was 10 P. M.

On rejoining the Major and his three sailors, Glenarvan warned them of the approaching storm, and advised them to secure themselves in their beds of branches as firmly as possible, for there was no doubt that after the first clap of thunder the wind would become unchained, and the OMBU would be violently shaken. Though they could not defend themselves from the waters above, they might at least keep out of the rushing current beneath.