days—very pleasant days—of language instruction from Milli. Dolf and Thig and others of the five came frequently, to note his progress and to talk with him and ask him questions.

A sitting room was provided for him, adjoining his sleeping quarters. Milli occupied quarters nearby.

Within a week he had mastered enough of the language of these people, for their strange history began to be intelligible to him.

In spite of the fact that the air here was at merely atmospheric pressure, nevertheless this place was one mile beneath the surface of the Pacific. Milli and her people lived in a city hollowed out of a reef of rocks, reinforced against the terrific weight of the water and filled with laboratory-made air. They had never been to the surface of the sea.

The fish with the human arms were their creators and their masters.

Professor Osborne had been right. The fish of the deep, having a head start on the rest of the world, had evolved to a perfectly unbelievable degree of intelligence. Centuries ago they had built for themselves the exact analog of George Abbot's bathysphere, and in it they had made much the same sort of exploring trips to the surface that he had made down into the deeps. But their spheres had been constructed to keep in, rather than to keep out, great pressure.

Their scientists had gathered a wealth of data as to conditions on the surface, and had even seen and studied human beings. But their insatiable scientific curiosity had led them to want to know more about the strange country above them and the strange persons who inhabited it. And so they set about breeding, in their own laboratories, creatures which should be as like as possible to those whom they had observed on the surface.