We descended from the tower and followed Kalliboas to a point on the north-eastern bank of the lake. The stream which entered here was of no great dimension, but even so, it flowed fast enough to have flooded the entire valley in a few weeks but for--as I imagine--the enormous degree of evaporation caused by the bone-dry climate, and the extensive irrigation works into which the water of the lake was deflected. Suddenly, with a heavy swirl, there arose in midstream a gigantic fish, which made straight for the bank where we stood. So startling was the creature's appearance and so swift its approach that I must confess for an instant I'd half an inclination to run, and I noticed Poyning took a quick step backwards from the water's edge. Then we realised our mistake. It was no fish at all, but a man, completely clad in a close-fitting diving costume; there were circles of transparent horn over the eyes, and gloved receptacles for the arms, but the legs went into one great sleeve stiffened to copy the tail of a fish; and we saw it was from this the diver got his power in swimming, an evolution he performed with singular ease and speed. How he was able to breathe and to sink at will we had no thought to examine then: our attention was very fully absorbed by a basket the man had been carrying in his hands under water and now laid on the bank. He rolled out, divested himself of the fish-like skin--which he was able to do without assistance--and made a profound obeisance to Kalliboas. 'This fellow,' said the latter, turning to us, 'is to our children the most beloved man in the city. It is his duty to swim to the bed of the river and the lake and gather for them these pretty playthings.' Kalliboas stooped over the basket, took out a handful of pebbles, and handed them to me. They were curious pebbles, looking like scarred rough glass, but now and then out of the roughness came a fierce flash of light as the sun's rays caught an exposed face. There was no room for doubt about these things. They were large diamonds. Poyning took one of them, as if to examine it, and as he did so I felt him nudge me very gently. 'Would it not be easier,' he said, 'to get the stones by dragging the river for them?' Then for the first and last time in our acquaintance Kalliboas chuckled. It was a grim chuckle, but the nearest approach to tenderness I ever knew him show. 'The children value the stones more for having been obtained in this way,' he said. 'Often they come to see Old Fish diving for them.' He scooped up another large handful and gave me. 'Take as many as you can carry,' he said, the grim half-smile still on his features. 'It may be that children in the city will ask you for them. It is true that in the world from which you have come men commit crimes to obtain these things, but you at least are above such temptation.'